impurities such as iron, sand and other metals [1]. Aluminum is durable, relatively soft, light weight, malleable and ductile metal with physical appearance ranging from silvery to dull gray depending on the roughness of the surface. Aluminum has almost one – third of the stiffness and density of steel. It is easily drawn, machined, cast and extruded. Aluminum is also a good electrical and thermal conductor. Aluminum and its alloys are very important material because of their wide use in many industries. They are used in the aviation, aerospace and automotive industries, in the production of military hardware, in ship building and household appliances [2–4]. Their usefulness is derived from their very good mechanical and physical properties such as their weight-to-high strength ratio, good machining properties, recyclability, and their outstanding corrosion resistance. The corrosion resistance of aluminum and its alloys is attributed to the formation of a stable protective thin film of aluminum oxide when exposed to the atmosphere. Aluminum alloys are therefore used widely as materials for electricity cables, bottle tops, food and beverage containers, and roofing sheets [5]. Despite the huge benefit of aluminum when compared to other metals, it is not always resistant to corrosion completely. When the environment is highly basic or acidic, the protective layer breakdown can occur and its instant renewal may not be fast enough to prevent corrosion [6–9]. Corrosion of aluminum leads to passivation of active cathode material, the electrical resistance of the solid product is increased and the electrolyte is contaminated by its soluble products and increases the self-discharge rate. In efforts to reduce aluminum corrosion, the main approach is to separate the aluminum metal from corrosive environments and this can be accomplished by means of corrosion inhibitors. Therefore, the ability of aluminum to resist corrosion attack in various environments is inadequate and a continuous search for methods for controlling this behavior remains important in the field of corrosion control.

at Vancouver, B.C., which examined the economics of corrosion and the role of corrosion management in establishing industry best practices [19]. Corrosion can be localized by forming a crack or pit, or expand across a wide area by uniformly corroding the surface [20]. Pitting corrosion takes place in materials with surface films protection like corrosion products, the metal exposed releases electrons easily and tiny pits is initiated by the reactions [21]. Galvanic corrosion usually occurs on the surface of metal which have more than one phase, in other for local cells to be set up on heterogeneous surface with different potentials. The preferential attack of grain boundaries without substantial attack of the grains themselves is called intergranular corrosion; it is often caused by the precipitation of fine intermetallics at grain boundaries [22]. Localized corrosion may possibly result in structure failure of metallic materials if it is allowed to reach critical levels [23]. Corrosion resistance of alloys has become a continuous research due to its severe consequences [24]. One of the most useful techniques in protecting and controlling metals against corrosion is the use of inhibitors, especially in

Gluconates as Corrosion Inhibitor of Aluminum in Various Corrosive Media

http://dx.doi.org/10.5772/intechopen.71467

159

The practice carried out to assess and predict the corrosion behavior in equipment and operational plant is known as corrosion monitoring. The objectives of corrosion monitoring are:

• To provide information based on the operational state of the equipment with the intent of avoiding unplanned shut-downs occurring from unforeseen deterioration of the plant. • To provide information on the operating variables and interrelation between corrosion

• To provide information that can be used to prevent potential disasters and safety failures

The principle behind corrosion protection is to influence the reactions which occur during corrosion, it being possible to control the corrosive agent and the package contents, and also the reaction itself in such a manner that corrosion is minimized. Corrosion protection is subdivided into three subtopics: passive, permanent and temporary corrosion protection.

Damage is prevented in passive corrosion protection by mechanically isolating the package contents from the aggressive corrosive agents, for example by using films or other coatings and protective layers. This type of corrosion protection changes neither the aggressiveness of the corrosive agent nor the general ability of the package contents to corrode; this is why this approach is known as passive corrosion protection. Corrosion may occur within a very short

time if the protective film or layer is destroyed at any point in time.

saline and acidic media.

**2. Corrosion control and monitoring**

processes to allow more efficient use of the plant.

• To assess process fluids contamination levels.

by plant inspection departments.

**2.1. Passive corrosion protection**

#### **1.2. Corrosion of metals**

The corrosion of metals is a serious problem in most industries. Corrosion phenomena, control and prevention are unavoidable major scientific issues that must be addressed daily as far as there are increasing needs of metallic materials in all facets of technological development [10]. Technological progresses require the use of materials in aggressive environments, such as corrosive atmospheres [11]. Corrosion is a degradation of metal due to environmental reactions dissolution; it is an electrochemical process and usually begins at the surface [12, 13]. As a result of daily encounters with corrosion problems such as; waste of valuable resources, costly maintenance, plant shutdowns, expensive overdesign, loss or contamination of products and reduction in efficiency; technological developments are impeded and safety endangered [14, 15]. The multifacet aspect of corrosion problems coupled with responsibilities associated with them only increase the complexity of the subject [16, 17]. This problem has caused the stimulation of many corrosion control research in various oil production facilities around the world [18]. The cost due to corrosion does not only increase rapidly, the quality of the products and the efficiency of the plants is also reduced. In the United States this amount to over 276 billion USD per year. The highest segments of the cost of corrosion are associated with utilities, transportation and infrastructure. Millions of dollars are lost each year because of corrosion including the cost of prevention and maintenance. NACE studies recently estimates global cost of corrosion at \$2.5 trillion annually at CORROSION 2016 conference held at Vancouver, B.C., which examined the economics of corrosion and the role of corrosion management in establishing industry best practices [19]. Corrosion can be localized by forming a crack or pit, or expand across a wide area by uniformly corroding the surface [20]. Pitting corrosion takes place in materials with surface films protection like corrosion products, the metal exposed releases electrons easily and tiny pits is initiated by the reactions [21]. Galvanic corrosion usually occurs on the surface of metal which have more than one phase, in other for local cells to be set up on heterogeneous surface with different potentials. The preferential attack of grain boundaries without substantial attack of the grains themselves is called intergranular corrosion; it is often caused by the precipitation of fine intermetallics at grain boundaries [22]. Localized corrosion may possibly result in structure failure of metallic materials if it is allowed to reach critical levels [23]. Corrosion resistance of alloys has become a continuous research due to its severe consequences [24]. One of the most useful techniques in protecting and controlling metals against corrosion is the use of inhibitors, especially in saline and acidic media.

## **2. Corrosion control and monitoring**

impurities such as iron, sand and other metals [1]. Aluminum is durable, relatively soft, light weight, malleable and ductile metal with physical appearance ranging from silvery to dull gray depending on the roughness of the surface. Aluminum has almost one – third of the stiffness and density of steel. It is easily drawn, machined, cast and extruded. Aluminum is also a good electrical and thermal conductor. Aluminum and its alloys are very important material because of their wide use in many industries. They are used in the aviation, aerospace and automotive industries, in the production of military hardware, in ship building and household appliances [2–4]. Their usefulness is derived from their very good mechanical and physical properties such as their weight-to-high strength ratio, good machining properties, recyclability, and their outstanding corrosion resistance. The corrosion resistance of aluminum and its alloys is attributed to the formation of a stable protective thin film of aluminum oxide when exposed to the atmosphere. Aluminum alloys are therefore used widely as materials for electricity cables, bottle tops, food and beverage containers, and roofing sheets [5]. Despite the huge benefit of aluminum when compared to other metals, it is not always resistant to corrosion completely. When the environment is highly basic or acidic, the protective layer breakdown can occur and its instant renewal may not be fast enough to prevent corrosion [6–9]. Corrosion of aluminum leads to passivation of active cathode material, the electrical resistance of the solid product is increased and the electrolyte is contaminated by its soluble products and increases the self-discharge rate. In efforts to reduce aluminum corrosion, the main approach is to separate the aluminum metal from corrosive environments and this can be accomplished by means of corrosion inhibitors. Therefore, the ability of aluminum to resist corrosion attack in various environments is inadequate and a continuous search for methods for controlling this behavior remains important in the field of corrosion control.

158 Aluminium Alloys – Recent Trends in Processing, Characterization, Mechanical behavior and Applications

The corrosion of metals is a serious problem in most industries. Corrosion phenomena, control and prevention are unavoidable major scientific issues that must be addressed daily as far as there are increasing needs of metallic materials in all facets of technological development [10]. Technological progresses require the use of materials in aggressive environments, such as corrosive atmospheres [11]. Corrosion is a degradation of metal due to environmental reactions dissolution; it is an electrochemical process and usually begins at the surface [12, 13]. As a result of daily encounters with corrosion problems such as; waste of valuable resources, costly maintenance, plant shutdowns, expensive overdesign, loss or contamination of products and reduction in efficiency; technological developments are impeded and safety endangered [14, 15]. The multifacet aspect of corrosion problems coupled with responsibilities associated with them only increase the complexity of the subject [16, 17]. This problem has caused the stimulation of many corrosion control research in various oil production facilities around the world [18]. The cost due to corrosion does not only increase rapidly, the quality of the products and the efficiency of the plants is also reduced. In the United States this amount to over 276 billion USD per year. The highest segments of the cost of corrosion are associated with utilities, transportation and infrastructure. Millions of dollars are lost each year because of corrosion including the cost of prevention and maintenance. NACE studies recently estimates global cost of corrosion at \$2.5 trillion annually at CORROSION 2016 conference held

**1.2. Corrosion of metals**

The practice carried out to assess and predict the corrosion behavior in equipment and operational plant is known as corrosion monitoring. The objectives of corrosion monitoring are:

The principle behind corrosion protection is to influence the reactions which occur during corrosion, it being possible to control the corrosive agent and the package contents, and also the reaction itself in such a manner that corrosion is minimized. Corrosion protection is subdivided into three subtopics: passive, permanent and temporary corrosion protection.

#### **2.1. Passive corrosion protection**

Damage is prevented in passive corrosion protection by mechanically isolating the package contents from the aggressive corrosive agents, for example by using films or other coatings and protective layers. This type of corrosion protection changes neither the aggressiveness of the corrosive agent nor the general ability of the package contents to corrode; this is why this approach is known as passive corrosion protection. Corrosion may occur within a very short time if the protective film or layer is destroyed at any point in time.

#### **2.2. Anti-corrosion coating protection**

The main purpose of permanent corrosion protection methods is to provide protection at the place of use. Machines are usually located in factory sheds and are protected from extreme variations in temperature, which frequently causes condensation. The stresses presented by biotic, chemical and climatic factors are relatively slight in this situation. Examples of permanent corrosion protection methods are: galvanization, tin plating, copper plating, coating and enameling.

inhibitors [34, 35]. The research on corrosion inhibition of aluminum alloy is ongoing due to this fact our research work focuses on the effectiveness of gluconates as corrosion inhibitors for

tion to this growing research area has necessitated the present investigation. Weight loss and potentiodynamic polarization techniques were used to examine the rate of deterioration. The effect of zinc gluconate and ferrous gluconate on the aluminum alloy surface in the test media was studied using high resolution scanning electron microscope equipped with energy dispersive spectroscopy (HR-SEM/EDS). Studies on surface characterization, adsorption mecha-

Petrochemical and refineries industries use different film-forming inhibitors to control wet corrosion. Water-soluble and water-soluble-oil-dispersible type inhibitors are continuously injected or oil-soluble and oil-soluble-water-dispersible type inhibitors are intermittently

Gathering pipelines, operating between oil and gas wells and processing plants, have corrosion problems similar to those in refineries and petrochemical plants. The flow regimes of multiphase fluids in pipelines influence the corrosion rate. At high flow rates, flow-induced corrosion and erosion-corrosion may occur, whereas at low flow rates, pitting corrosion is more common. Internal corrosion of pipelines is controlled by cleaning the pipeline and by

Potable water is frequently saturated with dissolved oxygen and is corrosive unless a protective film, or deposit, is formed. Cathodic inhibitors, such as calcium carbonate, silicates, polyphosphates, and zinc salts, are used to control potable water corrosion. Water is used in

Acids are broadly used in pickling, cleaning of oil refinery equipment, heat exchangers and in

Inhibitors are used in an automobile for two reasons which are; to reduce the corrosivity of fluid systems (internal corrosion), and to protect the metal surfaces exposed to the atmosphere (external corrosion). Internal corrosion is influenced by the coolants, flow, aeration, temperature, pressure, water impurities, corrosion products, operating conditions and maintenance of the system.

oil well acidizing. Mixed inhibitors are widely used to control acid corrosion.

nisms and electrochemical analysis of corroded materials were also carried out.

and 3.5% NaCl solutions. Attempt at making novel contribu-

Gluconates as Corrosion Inhibitor of Aluminum in Various Corrosive Media

http://dx.doi.org/10.5772/intechopen.71467

161

aluminum alloy in 0.5 M H2

*3.1.1. Petroleum production*

applied to control corrosion.

*3.1.3. Water*

*3.1.4. Acids*

*3.1.5. Automobile*

*3.1.2. Internal corrosion of steel pipelines*

adding continuous and/or batch inhibitors.

the cooling system in many industries.

SO4

**3.1. Industrial applications of corrosion inhibitors**

#### **2.3. Temporary corrosion protection**

The stresses occurring during handling, storage and transport are greater than those that occur at the place of use. Stresses manifested are; extreme variations in temperature, which result in a risk of condensation. In maritime transport, the elevated salt content of the air and water in the sea salt aerosols may cause damage, due to the strongly corrosion-promoting action of salts. The main temporary corrosion protection methods are as follows: desiccant method, protective coating method and corrosion Inhibitor methods.

Corrosion scientists are relentless in search of more and better efficient and cheap ways of mitigating the corrosion of metals and alloys. One of the ways of combating corrosion is the addition of inhibitors to the corroding environment. The various types of inhibitors can be classified as organic and inorganic. Corrosion inhibitors are used widely in industries to reduce or prevent corrosion rate of metals in acidic, alkaline media, and industrial processes such as acid descaling, acid pickling and cleaning of refinery equipment and oil well acidizing.

## **3. Corrosion inhibitors**

Certain substances which, when added to a corrosive system, modify the surface of the material to reduce the corrosion rate, are called inhibitors [25]. The use of chemical inhibitors to mitigate the rate of corrosion is quite varied. In the processing industries and oil extraction, inhibitors have always been considered to be one of the first ways against corrosion. Corrosion inhibitor performance has historically been described by two concepts namely: corrosion inhibitor availability and corrosion inhibitor efficiency. This essentially examines the ratio of the uninhibited and inhibited corrosion rates, and expresses this as a percentage. An inhibitor that reduced corrosion rates by a factor of 10 would be 90% efficient. This leads to the development of the concept of "availability of corrosion inhibitor." In this concept, performance is determined based on the summation of total metal loss over a period of time, assuming periods of uninhibited corrosion and inhibited corrosion. Corrosion availability concept is currently replacing the inhibitor efficiency concept with respect to use in corrosion inhibition concepts for systems design [26]. A great number of scientific researchers have responded to this need and it has generated increased research studies into the use of inhibitors. Compounds containing nitrogen as corrosion inhibitors have been investigated thoroughly by many authors; imidazole and benzimidazole derivatives [27–29], bipyrazole [30], quaternary ammonium salts [31], substituted aniline-N-salicylidenes [32], cationic surfactants [33], phosphorous containing inhibitors [34, 35]. The research on corrosion inhibition of aluminum alloy is ongoing due to this fact our research work focuses on the effectiveness of gluconates as corrosion inhibitors for aluminum alloy in 0.5 M H2 SO4 and 3.5% NaCl solutions. Attempt at making novel contribution to this growing research area has necessitated the present investigation. Weight loss and potentiodynamic polarization techniques were used to examine the rate of deterioration. The effect of zinc gluconate and ferrous gluconate on the aluminum alloy surface in the test media was studied using high resolution scanning electron microscope equipped with energy dispersive spectroscopy (HR-SEM/EDS). Studies on surface characterization, adsorption mechanisms and electrochemical analysis of corroded materials were also carried out.

#### **3.1. Industrial applications of corrosion inhibitors**

#### *3.1.1. Petroleum production*

**2.2. Anti-corrosion coating protection**

**2.3. Temporary corrosion protection**

**3. Corrosion inhibitors**

enameling.

The main purpose of permanent corrosion protection methods is to provide protection at the place of use. Machines are usually located in factory sheds and are protected from extreme variations in temperature, which frequently causes condensation. The stresses presented by biotic, chemical and climatic factors are relatively slight in this situation. Examples of permanent corrosion protection methods are: galvanization, tin plating, copper plating, coating and

160 Aluminium Alloys – Recent Trends in Processing, Characterization, Mechanical behavior and Applications

The stresses occurring during handling, storage and transport are greater than those that occur at the place of use. Stresses manifested are; extreme variations in temperature, which result in a risk of condensation. In maritime transport, the elevated salt content of the air and water in the sea salt aerosols may cause damage, due to the strongly corrosion-promoting action of salts. The main temporary corrosion protection methods are as follows: desiccant

Corrosion scientists are relentless in search of more and better efficient and cheap ways of mitigating the corrosion of metals and alloys. One of the ways of combating corrosion is the addition of inhibitors to the corroding environment. The various types of inhibitors can be classified as organic and inorganic. Corrosion inhibitors are used widely in industries to reduce or prevent corrosion rate of metals in acidic, alkaline media, and industrial processes such as acid descaling, acid pickling and cleaning of refinery equipment and oil well acidizing.

Certain substances which, when added to a corrosive system, modify the surface of the material to reduce the corrosion rate, are called inhibitors [25]. The use of chemical inhibitors to mitigate the rate of corrosion is quite varied. In the processing industries and oil extraction, inhibitors have always been considered to be one of the first ways against corrosion. Corrosion inhibitor performance has historically been described by two concepts namely: corrosion inhibitor availability and corrosion inhibitor efficiency. This essentially examines the ratio of the uninhibited and inhibited corrosion rates, and expresses this as a percentage. An inhibitor that reduced corrosion rates by a factor of 10 would be 90% efficient. This leads to the development of the concept of "availability of corrosion inhibitor." In this concept, performance is determined based on the summation of total metal loss over a period of time, assuming periods of uninhibited corrosion and inhibited corrosion. Corrosion availability concept is currently replacing the inhibitor efficiency concept with respect to use in corrosion inhibition concepts for systems design [26]. A great number of scientific researchers have responded to this need and it has generated increased research studies into the use of inhibitors. Compounds containing nitrogen as corrosion inhibitors have been investigated thoroughly by many authors; imidazole and benzimidazole derivatives [27–29], bipyrazole [30], quaternary ammonium salts [31], substituted aniline-N-salicylidenes [32], cationic surfactants [33], phosphorous containing

method, protective coating method and corrosion Inhibitor methods.

Petrochemical and refineries industries use different film-forming inhibitors to control wet corrosion. Water-soluble and water-soluble-oil-dispersible type inhibitors are continuously injected or oil-soluble and oil-soluble-water-dispersible type inhibitors are intermittently applied to control corrosion.

#### *3.1.2. Internal corrosion of steel pipelines*

Gathering pipelines, operating between oil and gas wells and processing plants, have corrosion problems similar to those in refineries and petrochemical plants. The flow regimes of multiphase fluids in pipelines influence the corrosion rate. At high flow rates, flow-induced corrosion and erosion-corrosion may occur, whereas at low flow rates, pitting corrosion is more common. Internal corrosion of pipelines is controlled by cleaning the pipeline and by adding continuous and/or batch inhibitors.

#### *3.1.3. Water*

Potable water is frequently saturated with dissolved oxygen and is corrosive unless a protective film, or deposit, is formed. Cathodic inhibitors, such as calcium carbonate, silicates, polyphosphates, and zinc salts, are used to control potable water corrosion. Water is used in the cooling system in many industries.

#### *3.1.4. Acids*

Acids are broadly used in pickling, cleaning of oil refinery equipment, heat exchangers and in oil well acidizing. Mixed inhibitors are widely used to control acid corrosion.

#### *3.1.5. Automobile*

Inhibitors are used in an automobile for two reasons which are; to reduce the corrosivity of fluid systems (internal corrosion), and to protect the metal surfaces exposed to the atmosphere (external corrosion). Internal corrosion is influenced by the coolants, flow, aeration, temperature, pressure, water impurities, corrosion products, operating conditions and maintenance of the system.

#### *3.1.6. Paints*

Finely divided inhibiting pigments are frequently incorporated in primers. These polar compounds displace water and orient themselves in such a way that the hydrophobic ends face the environment, thereby augmenting the bonding of the coatings on the surface.

and Igho [41] studied the effect of *Vernonia amygdalina* on the acidic corrosion of 3RS and 2S alloys using weight loss test. The results showed that the corrosion rate of the aluminum

concentration at 29°C. Umoren et al. [42] studied the corrosion inhibition of aluminum in hydrochloric acid medium using exudate gum from *Raphia hookeri* as inhibitor at 30–60°C by thermometric and weight loss methods. The experimental results showed that exudate gum is a good inhibitor of aluminum in hydrochloric acid medium and the efficiency of the inhibitor increases with an increase in concentration of the inhibitor but decreases with a rise in temperature. The authors concluded that *Raphia hookeri* performs as an inhibitor for aluminum corrosion in 0.1 M hydrochloric acid medium. Umoren and Solomon [38] investigated the influence of potassium iodide additives on the inhibition efficiency of *Aningeria robusta* extract for aluminum in 2 M hydrochloric medium using hydrogen evolution method at 30 and 60°C. Comparison between the corrosion rates data with and without additives was used to determine the inhibition efficiency by the authors. The result of the investigation showed that the *Aningeria robusta* extract is an inhibitor for acid corrosion of aluminum. *Lavandula angustifolia* was used as an inhibitor by [43]. The authors investigated the use of natural oil extracted from *Lavandula angustifolia* as an inhibitor for aluminum alloy in 3% sodium chloride medium using polarization measurements and weight loss techniques. The results showed that *L. angustifolia* oil acts as an effective inhibitor for the Al-3 Mg alloy corrosion in 3% NaCl medium at the temperature range studied. It was concluded that *Lavandula angustifolia* oil can be used to prevent pitting corrosion of aluminum. The combination of *Arachis hypogaea* natural oil was successfully used in the work of [37] as an inhibitor 2 M HNO3

2 M HCl acids solutions. Bark extract have been successfully studied as corrosion inhibitor for aluminum in 1 M NaOH by [44]. Comparative study of different plant extract has been carried out by [45]. In order to contribute to the ongoing research, the current research work is focused on analyzing the effectiveness of novel corrosion inhibitors ferrous gluconate (FG)

The potentiodynamic polarization behavior of the received aluminum sample in saline solution is shown in **Figure 1**, where the polarization curve can be seen and the data obtained can

In the sodium chloride solution, the aluminum sample gives a corrosion potential of −0.75893 V. The active corrosion path was formed as a result of the dissolution of the aluminum matrix. The surface of the tested aluminum coupon at different areas shows different dark shades, and this was examined by SEM/EDS. It is most likely that the darker areas are where the aluminum has not suffered severe corrosion from the sodium chloride, at those

and zinc gluconate (ZG) for the corrosion of aluminum alloy in acidic (0.5 M H2

**5. Gluconate as corrosion inhibition for aluminum alloy**

**5.1. Behavior of aluminum alloy substrate in sodium chloride solution**

and AlCl3

O3

and HCl solutions decreased with an increase in the exposure time

Gluconates as Corrosion Inhibitor of Aluminum in Various Corrosive Media

respectively. The authors concluded

http://dx.doi.org/10.5772/intechopen.71467

and HCl solution at 0.2 and 0.4 g/l

and

163

) and

SO4

coupons in the HNO3

saline (3.5% NaCl) media.

be seen in **Table 1**.

due to passivation of the surface by Al2

that the studied inhibitor is an excellent inhibitor in HNO3

#### **4. Corrosion prevention of aluminum alloy**

Gluconic acids are environmentally suitable non-toxic compounds. It is abundant in plants, fruits and other foodstuffs. Gluconic acid and its derivatives are used in the formulation of pharmaceuticals, foods, and cosmetics as mineral supplements to prevent the deficiency and as buffer salts. They are also used as ingredients in various hygienic products. In industrial applications, they are used for scale removal in metal cleanings, industrial and household cleaning compounds including mouth washer, metal finishing, water treatments, and as paper and textile auxiliaries. For these reasons, it is very useful to study the corrosion behavior of aluminum alloy in acidic and saline media using gluconates as inhibitor. Gluconate is a large hydrocarbon oxyanion [36], aluminum would be expected to anodize in the presence of this kind of ion. The aim of this research was to evaluate the effect of ferrous gluconate and zinc gluconate concentration on corrosion of aluminum alloy in different environments and to estimate optimal concentrations of ferrous gluconate and zinc gluconate required for satisfactory inhibition. Diverse researches carried out by different authors regarding the improvement of aluminum alloy using different inhibitors in various media have been attempted by different authors. Popoola et al. [37] confirm that in aggressive environment, the protective film on the surface of aluminum usually breakdown leading to initiation and further propagation of pits. The authors studied the corrosion inhibition of aluminum alloy in 2 M HCl and HNO3 with *Arachis hypogaea* natural oil as an inhibitor using potentiodynamic polarization and gravimetric techniques at 25°C. The obtained results showed that *Arachis hypogaea* oil in 2 M HCl and HNO3 -solutions decreased the corrosion rate of aluminum alloy at different concentrations of inhibitor considered. Umoren and Solomon [38] researched on the influence of bromide and iodide ions on the inhibitive effect of polyacrylamide (PA) on aluminum corrosion in HCl solution show that the halide additives synergistically increased the inhibition efficiency of polyacrylamide and the increase in inhibition efficiency was found to be more obvious in iodide than bromide ions. Obot and Obi-Egbedi [39] confirmed fluconazole (FLC) as a corrosion inhibitor for aluminum in hydrochloric acid solution. Garcia et al. [40] worked on the effect of solution pH on the anti-corrosion performance of different inhibitors K2 Cr2 O7 , CeCl3 , and Ce(dbp)3 on aluminum alloy (AA2024-T3) using the multi electrode and conventional potentiodynamic polarization methods. The results showed that the K2 Cr2 O7 at 10−4 M after 30 min of exposure time behaves as the best inhibitor across the studied pH range. The efficiency of the Ce(dbp)<sup>3</sup> and CeCl3 at 10−4 M was highly affected by the pH of the solution, where both cerium-based inhibitors gave similar protection to the K2 Cr2 . Onen et al. [5] analyzed the use of titanium (iv) oxide (TiO2 ) as an inhibitor for the corrosion of aluminum in H2 SO4 solution. Various researchers have come to the same conclusion that some compounds that exist naturally can be successfully used as corrosion inhibitors. Avwiri and Igho [41] studied the effect of *Vernonia amygdalina* on the acidic corrosion of 3RS and 2S alloys using weight loss test. The results showed that the corrosion rate of the aluminum coupons in the HNO3 and HCl solutions decreased with an increase in the exposure time due to passivation of the surface by Al2 O3 and AlCl3 respectively. The authors concluded that the studied inhibitor is an excellent inhibitor in HNO3 and HCl solution at 0.2 and 0.4 g/l concentration at 29°C. Umoren et al. [42] studied the corrosion inhibition of aluminum in hydrochloric acid medium using exudate gum from *Raphia hookeri* as inhibitor at 30–60°C by thermometric and weight loss methods. The experimental results showed that exudate gum is a good inhibitor of aluminum in hydrochloric acid medium and the efficiency of the inhibitor increases with an increase in concentration of the inhibitor but decreases with a rise in temperature. The authors concluded that *Raphia hookeri* performs as an inhibitor for aluminum corrosion in 0.1 M hydrochloric acid medium. Umoren and Solomon [38] investigated the influence of potassium iodide additives on the inhibition efficiency of *Aningeria robusta* extract for aluminum in 2 M hydrochloric medium using hydrogen evolution method at 30 and 60°C. Comparison between the corrosion rates data with and without additives was used to determine the inhibition efficiency by the authors. The result of the investigation showed that the *Aningeria robusta* extract is an inhibitor for acid corrosion of aluminum. *Lavandula angustifolia* was used as an inhibitor by [43]. The authors investigated the use of natural oil extracted from *Lavandula angustifolia* as an inhibitor for aluminum alloy in 3% sodium chloride medium using polarization measurements and weight loss techniques. The results showed that *L. angustifolia* oil acts as an effective inhibitor for the Al-3 Mg alloy corrosion in 3% NaCl medium at the temperature range studied. It was concluded that *Lavandula angustifolia* oil can be used to prevent pitting corrosion of aluminum. The combination of *Arachis hypogaea* natural oil was successfully used in the work of [37] as an inhibitor 2 M HNO3 and 2 M HCl acids solutions. Bark extract have been successfully studied as corrosion inhibitor for aluminum in 1 M NaOH by [44]. Comparative study of different plant extract has been carried out by [45]. In order to contribute to the ongoing research, the current research work is focused on analyzing the effectiveness of novel corrosion inhibitors ferrous gluconate (FG) and zinc gluconate (ZG) for the corrosion of aluminum alloy in acidic (0.5 M H2 SO4 ) and saline (3.5% NaCl) media.

## **5. Gluconate as corrosion inhibition for aluminum alloy**

*3.1.6. Paints*

HNO3

K2 Cr2 O7 , CeCl3

aluminum in H2

in 2 M HCl and HNO3

, and Ce(dbp)3

et al. [5] analyzed the use of titanium (iv) oxide (TiO2

range. The efficiency of the Ce(dbp)<sup>3</sup>

SO4

Finely divided inhibiting pigments are frequently incorporated in primers. These polar compounds displace water and orient themselves in such a way that the hydrophobic ends face

Gluconic acids are environmentally suitable non-toxic compounds. It is abundant in plants, fruits and other foodstuffs. Gluconic acid and its derivatives are used in the formulation of pharmaceuticals, foods, and cosmetics as mineral supplements to prevent the deficiency and as buffer salts. They are also used as ingredients in various hygienic products. In industrial applications, they are used for scale removal in metal cleanings, industrial and household cleaning compounds including mouth washer, metal finishing, water treatments, and as paper and textile auxiliaries. For these reasons, it is very useful to study the corrosion behavior of aluminum alloy in acidic and saline media using gluconates as inhibitor. Gluconate is a large hydrocarbon oxyanion [36], aluminum would be expected to anodize in the presence of this kind of ion. The aim of this research was to evaluate the effect of ferrous gluconate and zinc gluconate concentration on corrosion of aluminum alloy in different environments and to estimate optimal concentrations of ferrous gluconate and zinc gluconate required for satisfactory inhibition. Diverse researches carried out by different authors regarding the improvement of aluminum alloy using different inhibitors in various media have been attempted by different authors. Popoola et al. [37] confirm that in aggressive environment, the protective film on the surface of aluminum usually breakdown leading to initiation and further propagation of pits. The authors studied the corrosion inhibition of aluminum alloy in 2 M HCl and

 with *Arachis hypogaea* natural oil as an inhibitor using potentiodynamic polarization and gravimetric techniques at 25°C. The obtained results showed that *Arachis hypogaea* oil

concentrations of inhibitor considered. Umoren and Solomon [38] researched on the influence of bromide and iodide ions on the inhibitive effect of polyacrylamide (PA) on aluminum corrosion in HCl solution show that the halide additives synergistically increased the inhibition efficiency of polyacrylamide and the increase in inhibition efficiency was found to be more obvious in iodide than bromide ions. Obot and Obi-Egbedi [39] confirmed fluconazole (FLC) as a corrosion inhibitor for aluminum in hydrochloric acid solution. Garcia et al. [40] worked on the effect of solution pH on the anti-corrosion performance of different inhibitors

conventional potentiodynamic polarization methods. The results showed that the K2

and CeCl3

the solution, where both cerium-based inhibitors gave similar protection to the K2

at 10−4 M after 30 min of exposure time behaves as the best inhibitor across the studied pH

some compounds that exist naturally can be successfully used as corrosion inhibitors. Avwiri

on aluminum alloy (AA2024-T3) using the multi electrode and

solution. Various researchers have come to the same conclusion that

at 10−4 M was highly affected by the pH of

) as an inhibitor for the corrosion of

Cr2 O7

. Onen

Cr2

the environment, thereby augmenting the bonding of the coatings on the surface.

162 Aluminium Alloys – Recent Trends in Processing, Characterization, Mechanical behavior and Applications

**4. Corrosion prevention of aluminum alloy**

#### **5.1. Behavior of aluminum alloy substrate in sodium chloride solution**

The potentiodynamic polarization behavior of the received aluminum sample in saline solution is shown in **Figure 1**, where the polarization curve can be seen and the data obtained can be seen in **Table 1**.

In the sodium chloride solution, the aluminum sample gives a corrosion potential of −0.75893 V. The active corrosion path was formed as a result of the dissolution of the aluminum matrix. The surface of the tested aluminum coupon at different areas shows different dark shades, and this was examined by SEM/EDS. It is most likely that the darker areas are where the aluminum has not suffered severe corrosion from the sodium chloride, at those

**Figure 1.** Linear polarization curve for aluminum alloy in sodium chloride solution [46].

areas surface oxides layers have been formed that impeded corrosion. At the whitish areas aluminum dissolution must have occurred the chloride ion has penetrated the matrix of the aluminum surface. This was confirmed by the EDS analysis on the different areas which revealed that the darker areas had a high Al peak while the whitish areas consist of O, Na, S, Fe and C. In the border between the whitish and the darker areas there was a band of hole which seems to be associated to the dissolution of the Al alloy as a result of the aggressiveness of the sodium chloride. This hole did not exist on the as received sample [46] (**Figure 2**).

The result show the adsorption of the oxide film, formation of basic hydrochloric aluminum salt which separates from the lattice and goes into the system:

$$Al^{3+} + 4\text{ Cl}^- \rightarrow AlCl\_4^- \tag{1}$$

**5.2. Behavior of aluminum alloy substrate in H2**

**Figure 3.** Tafel polarization curve for aluminum alloy in H2

**Figure 2.** SEM/EDS spectra of corroded aluminum alloy in saline solution [46].

be seen in **Table 2**.

minum matrix.

**SO4**

The potentiodynamic polarization behavior of the as-received aluminum alloy sample in acid medium is shown in **Figure 3** where the polarization curve can be seen, the data obtained can

The linear polarization curve determines the active or passive characterization of aluminum alloy in acid solution. In the acid solution, the aluminum sample gives a corrosion potential of −0.55960 V. The active corrosion path was formed as a result of the dissolution of the alu-

SO4

acid solution [46].

 **acid medium**

Gluconates as Corrosion Inhibitor of Aluminum in Various Corrosive Media

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165

$$\text{Al}^{3+} + 2\text{ Cl}^{-} + 2\text{OH}^{-} \rightarrow \text{Al} \text{ (OH)}\_{2}\text{Cl} \tag{2}$$

The oxide film is thinned to the extent that aluminum ion can pass from the metal to the sodium chloride interface. The chloride ion gets entry by penetrating through the oxide film or diffusion of halide ion through the oxide film and attack the alloy.

**Table 1.** Polarization data for aluminum alloy in sodium chloride solution.

Gluconates as Corrosion Inhibitor of Aluminum in Various Corrosive Media http://dx.doi.org/10.5772/intechopen.71467 165

**Figure 2.** SEM/EDS spectra of corroded aluminum alloy in saline solution [46].

areas surface oxides layers have been formed that impeded corrosion. At the whitish areas aluminum dissolution must have occurred the chloride ion has penetrated the matrix of the aluminum surface. This was confirmed by the EDS analysis on the different areas which revealed that the darker areas had a high Al peak while the whitish areas consist of O, Na, S, Fe and C. In the border between the whitish and the darker areas there was a band of hole which seems to be associated to the dissolution of the Al alloy as a result of the aggressiveness of the sodium chloride. This hole did not exist on the as received sample [46] (**Figure 2**). The result show the adsorption of the oxide film, formation of basic hydrochloric aluminum

<sup>−</sup> → *AlC l*

<sup>−</sup> + 2*OH* → *Al* (*OH*)

The oxide film is thinned to the extent that aluminum ion can pass from the metal to the sodium chloride interface. The chloride ion gets entry by penetrating through the oxide film

**) βc (V/dec) βa (V/dec) LPR**

1 0.0 8.59E-06 0.050867 0.080038 1572.3 0.75893 0.277870

4

**Rp (Ωcm<sup>2</sup> )**

<sup>−</sup> (1)

<sup>2</sup> *Cl* (2)

**−Ecorr (V) CR (mm/yr)**

salt which separates from the lattice and goes into the system:

**Figure 1.** Linear polarization curve for aluminum alloy in sodium chloride solution [46].

164 Aluminium Alloys – Recent Trends in Processing, Characterization, Mechanical behavior and Applications

3+ + 2 *Cl*

or diffusion of halide ion through the oxide film and attack the alloy.

**Table 1.** Polarization data for aluminum alloy in sodium chloride solution.

*Al*3+ + 4 *Cl*

*Al*

**S/N C (% g/v) Icorr (A/cm2**

#### **5.2. Behavior of aluminum alloy substrate in H2 SO4 acid medium**

The potentiodynamic polarization behavior of the as-received aluminum alloy sample in acid medium is shown in **Figure 3** where the polarization curve can be seen, the data obtained can be seen in **Table 2**.

The linear polarization curve determines the active or passive characterization of aluminum alloy in acid solution. In the acid solution, the aluminum sample gives a corrosion potential of −0.55960 V. The active corrosion path was formed as a result of the dissolution of the aluminum matrix.

**Figure 3.** Tafel polarization curve for aluminum alloy in H2 SO4 acid solution [46].

**6.1. Aluminum alloy in saline medium with ferrous gluconate (FG) as inhibitor**

environment in the absence and presence of different concentrations of FG at 28°C.

**Figure 5** is the plot of weight loss against exposure time for aluminum alloy coupons in saline

Gluconates as Corrosion Inhibitor of Aluminum in Various Corrosive Media

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167

In the absence of FG, the weight loss increased with an increase in exposure time in 3.5% sodium chloride solution. The weight loss was 0.001 gm at the beginning of the analysis but increased with an increase in exposure time which gave a value of 0.011 gm after 28 days of exposure. In the presence of FG, the weight loss value was reduced given the highest value of 0.007 gm at the end of 28 days exposure time at all the concentrations of inhibitor studied. This clearly indicates a 36% reduction in weight loss value in the presence of FG when com-

**Figure 6** shows the graph of corrosion rate of aluminum alloy coupons in the absence and

Observation made indicates that corrosion rate of aluminum alloy reduced in the presence of all the different concentrations of FG considered. In the presence of 0.5% g/v concentration of FG, the corrosion rate value was 0.051 mm/yr at the end of 28 days exposure time compared with the absence of FG which gave 0.110 mm/yr at the end of 28 days of exposure [47, 49]. This shows 54% reduction in corrosion rate value compared with the absence of FG. It can be deduced that FG inhibits the corrosion of aluminum alloy in saline solution. Also shown in **Figure 7** is the graph of percentage inhibition efficiency (%IE) with exposure time in the pres-

A reduction in IE of FG from 100% depending on the concentration of FG added to the corrosive environment was observed. The inhibition efficiency at 0.5% g/v concentration

> Control 0.5%FG 1%FG 1.5%FG 2%FG

0 5 10 20 25 30

**Figure 5.** Weight loss versus exposure time for aluminum alloy immersed in 3.5% NaCl solution with varied ferrous

15 **Exposure time (Days)**

presence of varied concentrations of FG in 3.5% NaCl solution at 28°C.

*6.1.1. Weight loss method*

pared to the value in the absence of FG [47, 49].

ence of different concentrations of FG.

0

gluconate addition [47].

0.002 0.004 0.006 0.008 0.01 0.012

**Weight loss (mg)**

**Table 2.** Polarization data for aluminum alloy in 0.5 M H2 SO4 solution.

**Figure 4.** SEM/EDS spectra of corroded aluminum alloy in H2 SO4 acid solution [46].

A morphological study of the surface of aluminum specimen in acid solution was carried out by SEM after immersion in the test solution for 28 days at 28°C [46]. **Figure 4** shows the SEM images of the aluminum surface after 28 days immersion in 0.5 M H2 SO4 acid. A severely corroded surface was observed after immersion in the uninhibited system, due to corrosive attack of the acid solution. The corrosion product layer on the metal surface in uninhibited 0.5 M H2 SO4 acid and the corrosion damage is clearly visible on the metal surface. The oxide film is thinned to the extent that aluminum ions can pass from the aluminum alloy to the solution interface.

$$\text{Al}\_2\text{O}\_3 + 3\,\text{H}\_2\text{SO}\_4 \to \text{Al}\_2\{\text{SO}\_4\}\_3 + 3\,\text{H}\_2\text{O}\tag{3}$$

The sulfuric ion gets entry by penetration through the oxide film and attack the metal.

## **6. Characterization of inhibited aluminum alloy in saline (3.5% NaCl) medium**

The obtained results from weight loss and potentiodynamic polarization methods at different concentrations of ferrous gluconate (FG), zinc gluconate (ZG) and the synergistic effect of the two inhibitors in saline solution at 28°C are represented in Figures below.

#### **6.1. Aluminum alloy in saline medium with ferrous gluconate (FG) as inhibitor**

#### *6.1.1. Weight loss method*

A morphological study of the surface of aluminum specimen in acid solution was carried out by SEM after immersion in the test solution for 28 days at 28°C [46]. **Figure 4** shows the SEM

SO4

acid solution [46].

**) βc (V/dec) βa (V/dec) LPR**

166 Aluminium Alloys – Recent Trends in Processing, Characterization, Mechanical behavior and Applications

1 0.0 1.73E-05 0.025551 0.12493 532.51 0.33054 0.55960

SO4

solution.

**Rp (Ωcm<sup>2</sup> )**

corroded surface was observed after immersion in the uninhibited system, due to corrosive attack of the acid solution. The corrosion product layer on the metal surface in uninhibited

film is thinned to the extent that aluminum ions can pass from the aluminum alloy to the

*SO*<sup>4</sup> → *Al*2(*SO*4)

The obtained results from weight loss and potentiodynamic polarization methods at different concentrations of ferrous gluconate (FG), zinc gluconate (ZG) and the synergistic effect of the

The sulfuric ion gets entry by penetration through the oxide film and attack the metal.

**6. Characterization of inhibited aluminum alloy in saline (3.5%**

two inhibitors in saline solution at 28°C are represented in Figures below.

acid and the corrosion damage is clearly visible on the metal surface. The oxide

3

SO4

**−Ecorr (V) CR (mm/yr)**

+ 3 *H*<sup>2</sup> *O* (3)

acid. A severely

images of the aluminum surface after 28 days immersion in 0.5 M H2

0.5 M H2

SO4

**S/N C (% g/v) Icorr (A/cm2**

**Table 2.** Polarization data for aluminum alloy in 0.5 M H2

*Al*<sup>2</sup> *O*<sup>3</sup> + 3 *H*<sup>2</sup>

**Figure 4.** SEM/EDS spectra of corroded aluminum alloy in H2

solution interface.

**NaCl) medium**

**Figure 5** is the plot of weight loss against exposure time for aluminum alloy coupons in saline environment in the absence and presence of different concentrations of FG at 28°C.

In the absence of FG, the weight loss increased with an increase in exposure time in 3.5% sodium chloride solution. The weight loss was 0.001 gm at the beginning of the analysis but increased with an increase in exposure time which gave a value of 0.011 gm after 28 days of exposure. In the presence of FG, the weight loss value was reduced given the highest value of 0.007 gm at the end of 28 days exposure time at all the concentrations of inhibitor studied. This clearly indicates a 36% reduction in weight loss value in the presence of FG when compared to the value in the absence of FG [47, 49].

**Figure 6** shows the graph of corrosion rate of aluminum alloy coupons in the absence and presence of varied concentrations of FG in 3.5% NaCl solution at 28°C.

Observation made indicates that corrosion rate of aluminum alloy reduced in the presence of all the different concentrations of FG considered. In the presence of 0.5% g/v concentration of FG, the corrosion rate value was 0.051 mm/yr at the end of 28 days exposure time compared with the absence of FG which gave 0.110 mm/yr at the end of 28 days of exposure [47, 49]. This shows 54% reduction in corrosion rate value compared with the absence of FG. It can be deduced that FG inhibits the corrosion of aluminum alloy in saline solution. Also shown in **Figure 7** is the graph of percentage inhibition efficiency (%IE) with exposure time in the presence of different concentrations of FG.

A reduction in IE of FG from 100% depending on the concentration of FG added to the corrosive environment was observed. The inhibition efficiency at 0.5% g/v concentration

**Figure 5.** Weight loss versus exposure time for aluminum alloy immersed in 3.5% NaCl solution with varied ferrous gluconate addition [47].

**Figure 6.** Corrosion rate versus exposure time for aluminum alloy immersed in 3.5% NaCl solution with varied ferrous gluconate addition [47].

*6.1.3. Microstructural characterization of FG inhibited aluminum alloy in saline medium*

R² = 0.949(192h) 0

y = 0.5x R² = 1(96h)

0123456

**C(%g/v)**

**Figure 8.** Langmuir isotherm for the adsorption of different concentrations of FG on aluminum alloy surface in 3.5%

gluconate constituent [47].

NaCl solution obtained at 28°C [47].

y = 0.5x R² = 1(48h)

> y = 0.735x - 0.279 R² = 0.981(144h)

1

2

**C/θ**

3

4

The morphology of the test sample showing the inhibitive action of ferrous gluconate in saline solution with 1.0% g/v concentration of FG after weight loss experiment is shown in **Figure 9**. The severity of the damage is much less when compared with the morphology of the sample in the absence of FG. The effective corrosion inhibition of FG could be attributed to the film formed on the aluminum alloy surface which acts as a barrier between the aluminum alloy and the corrosive environment boundary, thereby preventing further corrosion reaction. From the EDS in **Figure 9**, the presence of oxygen and other elements is as a result of ferrous

y = 0.506x + 0.085

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48h 96h 144h 192h 169

In the presence of 2.0% g/v concentration of FG, the corrosion is slightly reduced with little corrosion product on the aluminum alloy surface when compared with the morphology of the aluminum alloy in the absence of FG. This clearly revealed that FG is a corrosion inhibitor for the aluminum alloy in acidic solution. The effective corrosion inhibition of FG could

**Figure 9.** SEM/EDS spectra of corroded aluminum alloy in the presence of FG [47].

of FG reduced to 54%, 1.0% g/v reduced to 46%, 1.5% g/v reduced to 45% and 2.0% g/v reduced to 44% at the end of 28 days exposure time to the corrosive environment. The optimum inhibition efficiency was observed at 1.0% g/v concentration of FG in 3.5% NaCl solution at 28°C.

#### *6.1.2. Adsorption studies*

The Langmuir adsorption isotherm was found to best describe the adsorption behavior of FG as inhibitor. Plot C/against C yield straight lines with regression coefficient, R<sup>2</sup> equals 1. The results plotted in **Figure 8** suggest that FG in 3.5% NaCl solution at 28°C obeyed Langmuir adsorption isotherm.

**Figure 7.** Inhibition efficiency versus exposure time for aluminum alloy immersed in 3.5% NaCl solution with varied ferrous gluconate addition [47].

Gluconates as Corrosion Inhibitor of Aluminum in Various Corrosive Media http://dx.doi.org/10.5772/intechopen.71467 169

**Figure 8.** Langmuir isotherm for the adsorption of different concentrations of FG on aluminum alloy surface in 3.5% NaCl solution obtained at 28°C [47].

#### *6.1.3. Microstructural characterization of FG inhibited aluminum alloy in saline medium*

0 0.05 0.1 0.15 0.2 0.25 0.3

gluconate addition [47].

solution at 28°C.

*6.1.2. Adsorption studies*

0%

ferrous gluconate addition [47].

20%

40%

**Inhibition efficiency (%)**

60%

80%

100%

adsorption isotherm.

**Corrosion rate (mm/yr)**

0 4 8 12 16 20 24 28

168 Aluminium Alloys – Recent Trends in Processing, Characterization, Mechanical behavior and Applications

 **Exposure time (days)**

**Figure 6.** Corrosion rate versus exposure time for aluminum alloy immersed in 3.5% NaCl solution with varied ferrous

of FG reduced to 54%, 1.0% g/v reduced to 46%, 1.5% g/v reduced to 45% and 2.0% g/v reduced to 44% at the end of 28 days exposure time to the corrosive environment. The optimum inhibition efficiency was observed at 1.0% g/v concentration of FG in 3.5% NaCl

The Langmuir adsorption isotherm was found to best describe the adsorption behavior of FG

results plotted in **Figure 8** suggest that FG in 3.5% NaCl solution at 28°C obeyed Langmuir

as inhibitor. Plot C/against C yield straight lines with regression coefficient, R<sup>2</sup>

0 4 8 12 16 20 24 28

 **Exposure time (Days)**

**Figure 7.** Inhibition efficiency versus exposure time for aluminum alloy immersed in 3.5% NaCl solution with varied

Control 0.5%FG 1%FG 1.5%FG 2%FG

> 0.5%FG 1%FG 1.5%FG 2%FG

equals 1. The

The morphology of the test sample showing the inhibitive action of ferrous gluconate in saline solution with 1.0% g/v concentration of FG after weight loss experiment is shown in **Figure 9**. The severity of the damage is much less when compared with the morphology of the sample in the absence of FG. The effective corrosion inhibition of FG could be attributed to the film formed on the aluminum alloy surface which acts as a barrier between the aluminum alloy and the corrosive environment boundary, thereby preventing further corrosion reaction. From the EDS in **Figure 9**, the presence of oxygen and other elements is as a result of ferrous gluconate constituent [47].

In the presence of 2.0% g/v concentration of FG, the corrosion is slightly reduced with little corrosion product on the aluminum alloy surface when compared with the morphology of the aluminum alloy in the absence of FG. This clearly revealed that FG is a corrosion inhibitor for the aluminum alloy in acidic solution. The effective corrosion inhibition of FG could

**Figure 9.** SEM/EDS spectra of corroded aluminum alloy in the presence of FG [47].

be attributed to the film formed on the surface of the sample. The EDS in **Figure 9** clearly shows the presence of carbon, oxygen indicating the formation of oxide films as confirmed by Raman spectroscopy. Other elements are also present which is as a result of ferrous gluconate constituent.

#### *6.1.4. Potentiodynamic polarization method*

**Table 3** shows the electrochemical corrosion parameters that is, potentiodynamic polarization-corrosion potential (Ecorr), linear polarization resistance (Rp), anodic and cathodic Tafel slopes (βa, βc), corrosion rate (CR) and potentiodynamic polarization corrosion-current density (icorr) obtained by extrapolation of the Tafel lines.

**Figure 10** gives the potentiodynamic polarization curves for the inhibition of aluminum alloy in the absence and presence of different concentrations of ZG in 0.5 molar sulfuric acid solutions at 28°C. From **Table 3**, it can be concluded that the corrosion current density (icorr) values reduced in the presence of all the concentrations of ZG studied. The anodic and cathodic values were observed to change in the presence of all the different concentrations of ZG studied in 0.5 M H2 SO4 solution. The polarization resistance (Rp) values increased and corrosion rate (CR) values decreased in the presence of inhibitor. Also, no definite trend was observed in the corrosion potential (Ecorr) values in the presence of inhibitor [47]. This result showed the influence of ZG on aluminum alloy in 0.5 M H2 SO4 solution and the ZG acts as a mixed type inhibitor.

at 0.5:0.5, 1.0:1.0, 1.5:1.5 and 2.0:2.0 g/v concentrations of inhibitors respectively. These values translated to 27% for 0.5:0.5 g/v, 32% for 1.0:1.0 g/v, 41% for 1.5:1.5 g/v and 46% for 2.0:2.0 g/v when the weight loss values in the presence of inhibitors were compared with the values in the absence of inhibitors. The Figure also denotes that increase in concentration of the inhibi-

SO4

Gluconates as Corrosion Inhibitor of Aluminum in Various Corrosive Media

at 28°C in the absence and presence of different concentrations of FG and ZG are presented in **Figure 11**. The Figure shows that in the absence of inhibitors, the corrosion rate of aluminum alloy decreased from 0.395 to 0.346 mm/yr after 28 days exposure time to the corrosive envi-

SO4

Control

solution with varied ferrous

SO4

0.5%FG-0.5%ZG 1%FG-1%ZG 1.5%FG-1.5%ZG 2%FG-2%ZG

solution in the absence and presence of different

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solution

tor leads to a decrease in the weight loss of the aluminum alloy coupon.

**Figure 10.** Tafel polarization curves for aluminum alloy in 0.5 M H2

ronment (**Figure 12**).

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04

gluconate and zinc gluconate additions [46].

**Weight loss (mg)**

concentrations of ZG at 28°C [48].

The variation of corrosion rates of aluminum alloy coupons exposed to 0.5 M H2

0 5 10 15 20 25 30

**Figure 11.** Weight loss versus exposure time for aluminum alloy immersed in 0.5 M H2

**Exposure time (Days)**

#### **6.2. Synergetic effect of the two inhibitors (FG+ZG) on aluminum alloy in H<sup>2</sup> SO4 acid medium**

#### *6.2.1. Weight loss method*

**Figure 11** shows the variation of weight loss with exposure time for aluminum alloy coupons in 0.5 molar sulfuric acid solution in the absence and presence of different concentrations of FG and ZG in the same proportion at 28°C. The Figure shows an increase in weight loss value in the absence of inhibitors with an increase in exposure time. In the presence of inhibitors, there was a decrease in weight loss of the aluminum alloy coupons with the following values after 28 days exposure time to the corrosive medium; 0.027 gm, 0.025 gm, 0.022 gm and 0.020 gm

**Table 3.** Polarization data for ZG inhibited aluminum alloy in 0.5 M H2 SO4 solution.

be attributed to the film formed on the surface of the sample. The EDS in **Figure 9** clearly shows the presence of carbon, oxygen indicating the formation of oxide films as confirmed by Raman spectroscopy. Other elements are also present which is as a result of ferrous gluconate

170 Aluminium Alloys – Recent Trends in Processing, Characterization, Mechanical behavior and Applications

**Table 3** shows the electrochemical corrosion parameters that is, potentiodynamic polarization-corrosion potential (Ecorr), linear polarization resistance (Rp), anodic and cathodic Tafel slopes (βa, βc), corrosion rate (CR) and potentiodynamic polarization corrosion-current den-

**Figure 10** gives the potentiodynamic polarization curves for the inhibition of aluminum alloy in the absence and presence of different concentrations of ZG in 0.5 molar sulfuric acid solutions at 28°C. From **Table 3**, it can be concluded that the corrosion current density (icorr) values reduced in the presence of all the concentrations of ZG studied. The anodic and cathodic values were observed to change in the presence of all the different concentrations of ZG studied in

values decreased in the presence of inhibitor. Also, no definite trend was observed in the corrosion potential (Ecorr) values in the presence of inhibitor [47]. This result showed the influence

**Figure 11** shows the variation of weight loss with exposure time for aluminum alloy coupons in 0.5 molar sulfuric acid solution in the absence and presence of different concentrations of FG and ZG in the same proportion at 28°C. The Figure shows an increase in weight loss value in the absence of inhibitors with an increase in exposure time. In the presence of inhibitors, there was a decrease in weight loss of the aluminum alloy coupons with the following values after 28 days exposure time to the corrosive medium; 0.027 gm, 0.025 gm, 0.022 gm and 0.020 gm

**) βc (V/dec) βa (V/dec) LPR**

 0.0 1.73E-05 0.025551 0.124930 5.33E+02 0.33054 0.559600 0.5 6.46E-06 0.054932 0.032904 1.38E+03 0.33054 0.209090 1.0 5.43E-06 0.042048 0.035871 1.55E+03 0.33054 0.175710 1.5 6.30E-09 0.892180 1.727600 4.06E+07 0.34318 0.000206 2.0 3.78E-06 0.172780 0.072640 5.87E+03 0.35751 0.123690

**Table 3.** Polarization data for ZG inhibited aluminum alloy in 0.5 M H2

SO4

**6.2. Synergetic effect of the two inhibitors (FG+ZG) on aluminum alloy in H<sup>2</sup>**

solution. The polarization resistance (Rp) values increased and corrosion rate (CR)

solution and the ZG acts as a mixed type inhibitor.

**Rp (Ωcm<sup>2</sup> )**

SO4

solution.

**SO4**

**−Ecorr (V) CR (mm/yr)**

constituent.

0.5 M H2

**acid medium**

*6.2.1. Weight loss method*

**S/N C (% g/v) Icorr (A/cm2**

SO4

of ZG on aluminum alloy in 0.5 M H2

*6.1.4. Potentiodynamic polarization method*

sity (icorr) obtained by extrapolation of the Tafel lines.

**Figure 10.** Tafel polarization curves for aluminum alloy in 0.5 M H2 SO4 solution in the absence and presence of different concentrations of ZG at 28°C [48].

at 0.5:0.5, 1.0:1.0, 1.5:1.5 and 2.0:2.0 g/v concentrations of inhibitors respectively. These values translated to 27% for 0.5:0.5 g/v, 32% for 1.0:1.0 g/v, 41% for 1.5:1.5 g/v and 46% for 2.0:2.0 g/v when the weight loss values in the presence of inhibitors were compared with the values in the absence of inhibitors. The Figure also denotes that increase in concentration of the inhibitor leads to a decrease in the weight loss of the aluminum alloy coupon.

The variation of corrosion rates of aluminum alloy coupons exposed to 0.5 M H2 SO4 solution at 28°C in the absence and presence of different concentrations of FG and ZG are presented in **Figure 11**. The Figure shows that in the absence of inhibitors, the corrosion rate of aluminum alloy decreased from 0.395 to 0.346 mm/yr after 28 days exposure time to the corrosive environment (**Figure 12**).

**Figure 11.** Weight loss versus exposure time for aluminum alloy immersed in 0.5 M H2 SO4 solution with varied ferrous gluconate and zinc gluconate additions [46].

*6.2.2. Adsorption studies*

regression coefficient, R<sup>2</sup>

SO4

aluminum alloy in 0.5 M H2

0

SO4

0.5 M H2

1

2

**C/θ**

4

*6.2.3. Potentiodynamic polarization method*

presence of different concentrations of FG and ZG at 28°C.

SO4

y = 0.4448x + 0.184

R² = 0.9898 3

solution obtained at 28°C [46].

in 0.5 M H2

The Langmuir adsorption isotherm provides the best description for the adsorption behavior of the synergistic effect of FG and ZG as inhibitors. Plot C/against C yield a straight line with

**Table 4** shows the electrochemical corrosion kinetics parameters: polarization resistance (Rp), potentiodynamic polarization-corrosion potential (Ecorr), potentiodynamic polarization corrosion-current density (icorr), corrosion rate (CR), anodic and cathodic Tafel slopes (βa and βc) obtained by extrapolation of the Tafel lines. **Figure 15** shows the cathodic and anodic polarization curves obtained for aluminum alloy in 0.5 molar sulfuric acid solution in the absence and

The results showed a decrease in corrosion current density (icorr) and corrosion rate (CR) values in the presence of different concentrations of inhibitors studied. The corrosion potential (Ecorr) and polarization resistance (Rp) values increased in the presence of inhibitors. Shifts in anodic and cathodic region suggest the inhibitor is a mixed type corrosion inhibitors for

The percentage inhibition efficiency (%IE) of aluminum alloy in 3.5% sodium chloride solution and 0.5 molar sulfuric acid environments in the presence of different concentrations of FG, ZG and the synergistic effect of the two inhibitors was obtained from weight loss and potentiodynamic

012345

**C(%g/v)**

**Figure 14.** Langmuir isotherm for the adsorption of different concentrations of FG and ZG on aluminum alloy surface in

48h

solution at 28°C.

**6.3. Correlation between experimental results and analyses (aluminum)**

*6.3.1. Weight loss and electrochemical corrosion test methods (aluminum)*

solution at 28°C obeyed Langmuir adsorption isotherm.

close to 1. The result plotted in **Figure 14** suggests that the inhibitors

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**Figure 12.** Corrosion rate versus exposure time for aluminum alloy immersed in 0.5 M H2 SO4 solution with varied ferrous gluconate and zinc gluconate additions [46, 50–51].

The graph shows a sinusoidal trend. In the presence of inhibitors, the corrosion rate values was reduced from 0.346 to 0.272 mm/yr at 0.5:0.5 g/v concentration of FG-ZG, 0.268 mm/yr at 1.0:1.0 g/v, 0.345 mm/yr at 1.5:1.5 g/v and 0.175 mm/yr at 2.0:2.0 g/v. The percentage reduction in the corrosion rate value of aluminum alloy after 28 days of exposure in the presence of different concentrations of inhibitors are 21% for 0.5:0.5 g/v, 23% for 1.0:1.0 g/v, 0.3% for 1.5:1.5 g/v and 49% at 2.0:2.0 g/v.

**Figure 13** shows the variation of percentage inhibition efficiency (%IE) against exposure time with different concentrations of inhibitors at 28°C. From the results, it was observed that the inhibition efficiency increased with an increase in the concentration of the inhibitors. The optimum inhibition efficiency was observed at 0.5 g/v concentration of the inhibitors.

**Figure 13.** Inhibition efficiency versus exposure time for aluminum alloy immersed in 0.5 M H<sup>2</sup> SO4 solution with varied ferrous gluconate and zinc gluconate additions [46].

#### *6.2.2. Adsorption studies*

The graph shows a sinusoidal trend. In the presence of inhibitors, the corrosion rate values was reduced from 0.346 to 0.272 mm/yr at 0.5:0.5 g/v concentration of FG-ZG, 0.268 mm/yr at 1.0:1.0 g/v, 0.345 mm/yr at 1.5:1.5 g/v and 0.175 mm/yr at 2.0:2.0 g/v. The percentage reduction in the corrosion rate value of aluminum alloy after 28 days of exposure in the presence of different concentrations of inhibitors are 21% for 0.5:0.5 g/v, 23% for 1.0:1.0 g/v, 0.3% for

 **Exposure time (Days)**

Control

SO4

0.5%FG-0.5%ZG 1%FG-1%ZG 1.5%FG-1.5%ZG 2%FG-2%ZG

solution with varied

0.5%FG-0.5%ZG 1%FG-1%ZG 1.5%FG-1.5%ZG 2%FG-2%ZG

solution with varied

SO4

0 4 8 12 16 20 24 28

172 Aluminium Alloys – Recent Trends in Processing, Characterization, Mechanical behavior and Applications

**Figure 12.** Corrosion rate versus exposure time for aluminum alloy immersed in 0.5 M H2

**Figure 13** shows the variation of percentage inhibition efficiency (%IE) against exposure time with different concentrations of inhibitors at 28°C. From the results, it was observed that the inhibition efficiency increased with an increase in the concentration of the inhibitors. The opti-

mum inhibition efficiency was observed at 0.5 g/v concentration of the inhibitors.

0 4 8 12 16 20 24 28

**Figure 13.** Inhibition efficiency versus exposure time for aluminum alloy immersed in 0.5 M H<sup>2</sup>

 **Exposure time (Days)**

1.5:1.5 g/v and 49% at 2.0:2.0 g/v.

0%

ferrous gluconate and zinc gluconate additions [46].

20%

40%

**Inhibition efficiency (%)**

60%

80%

100%

ferrous gluconate and zinc gluconate additions [46, 50–51].

0

0.1

0.2

0.3

**Corrosion rate (mm/yr)**

0.4

0.5

0.6

The Langmuir adsorption isotherm provides the best description for the adsorption behavior of the synergistic effect of FG and ZG as inhibitors. Plot C/against C yield a straight line with regression coefficient, R<sup>2</sup> close to 1. The result plotted in **Figure 14** suggests that the inhibitors in 0.5 M H2 SO4 solution at 28°C obeyed Langmuir adsorption isotherm.

#### *6.2.3. Potentiodynamic polarization method*

**Table 4** shows the electrochemical corrosion kinetics parameters: polarization resistance (Rp), potentiodynamic polarization-corrosion potential (Ecorr), potentiodynamic polarization corrosion-current density (icorr), corrosion rate (CR), anodic and cathodic Tafel slopes (βa and βc) obtained by extrapolation of the Tafel lines. **Figure 15** shows the cathodic and anodic polarization curves obtained for aluminum alloy in 0.5 molar sulfuric acid solution in the absence and presence of different concentrations of FG and ZG at 28°C.

The results showed a decrease in corrosion current density (icorr) and corrosion rate (CR) values in the presence of different concentrations of inhibitors studied. The corrosion potential (Ecorr) and polarization resistance (Rp) values increased in the presence of inhibitors. Shifts in anodic and cathodic region suggest the inhibitor is a mixed type corrosion inhibitors for aluminum alloy in 0.5 M H2 SO4 solution at 28°C.

#### **6.3. Correlation between experimental results and analyses (aluminum)**

#### *6.3.1. Weight loss and electrochemical corrosion test methods (aluminum)*

The percentage inhibition efficiency (%IE) of aluminum alloy in 3.5% sodium chloride solution and 0.5 molar sulfuric acid environments in the presence of different concentrations of FG, ZG and the synergistic effect of the two inhibitors was obtained from weight loss and potentiodynamic

**Figure 14.** Langmuir isotherm for the adsorption of different concentrations of FG and ZG on aluminum alloy surface in 0.5 M H2 SO4 solution obtained at 28°C [46].

the aluminum alloy in sulfuric acid solution compared to sodium chloride solution, which implied that the corrosion rate in acidic medium is higher when compared to corrosion rate

Gluconates as Corrosion Inhibitor of Aluminum in Various Corrosive Media

http://dx.doi.org/10.5772/intechopen.71467

175

• The aluminum alloy exhibited similar corrosion behavior in the presence of different concentrations of inhibitors in the solution studied, with different corrosion resistances in the different solutions which was confirmed from the similar trend from corrosion rates and inhibition efficiency of the materials from weight loss and potentiodynamic polarization curves.

• In saline environment in the presence of different concentration of inhibitors, the corrosion resistant of aluminum alloy was significantly different, which was evident by their corrosion rates and inhibition efficiency values. FG performed best at 1.0% g/v concentration in 3.5% NaCl solution which gave inhibition efficiency value of 100% from the beginning of the analysis to the 8th day of exposure time to the corrosive medium. ZG performed best at 2.0% g/v concentration which gives inhibition efficiency value of 100% from the beginning of the analysis to the 14th day of exposure time to the corrosive solution and the inhibition efficiency of the synergism of the two inhibitors was 100% from the beginning of the analy-

• It could be concluded that ZG performed best in 3.5% NaCl solution. The inhibitors performed

tained from the weight loss and potentiodynamic polarization methods show good agreement. • The main task of this research work has been accomplished. The optimum concentrations for the application of the inhibitors which should be useful guide for corrosion engineers

• It can be seen from above that FG, ZG and FG+ZG acts as a good corrosion inhibitor for aluminum alloy in saline and acid environments with the following final deduction: Aluminum alloy: in both test environments, the inhibitive performances of the inhibitors are excellent. Finally, the inhibitors have been established to be practically reliable and effective as demonstrated by the performance characteristics of the inhibitors that were used in this study.

Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of

solution. The corrosion rates and inhibition efficiency values ob-

in sodium chloride medium in the presence and absence of inhibitors.

The following conclusions have been drawn from this research;

sis to the 10th day of exposure time to the corrosive medium.

SO4

Omotayo Sanni\* and Abimbola Patricia Popoola

Technology, Pretoria, South Africa

\*Address all correspondence to<EMAIL_ADDRESS>
**7. Conclusions**

fairly well in 0.5 M H2

have been obtained.

**Author details**

**Table 4.** Polarization data for FG and ZG inhibited aluminum alloy in 0.5 M H2 SO4 solution.

polarization methods. The data computed for the %IE using linear polarization resistance (LPR), potentiodynamic polarization-corrosion rate (PP-CR), potentiodynamic polarization-corrosion current density (PP-icorr) and weight loss method (WLM) are presented in the Figures above at different concentrations of inhibitors studied. From the given graphs, it is evident that obtained data from the different methods are in good correlation at all the concentrations of inhibitors studied.

#### *6.3.2. Surfaces analyses (aluminum alloy)*

From the SEM/EDS micrographs, aluminum alloy in acidic medium was observed to be more corrosive than aluminum alloy in sodium chloride medium after the immersion tests in both environments in the absence of inhibitors. Significant difference in the morphology of the as-received and the corroded samples of aluminum alloy in the absence and presence of inhibitors revealed that the inhibitors was able to hinder the dissolution of aluminum alloy in all the environments investigated. More uniform films were observed on the surfaces of

**Figure 15.** Tafel polarization curves for aluminum alloy in 0.5 M H2 SO4 medium in the absence and presence of different concentrations of FG and ZG at 28°C [46].

the aluminum alloy in sulfuric acid solution compared to sodium chloride solution, which implied that the corrosion rate in acidic medium is higher when compared to corrosion rate in sodium chloride medium in the presence and absence of inhibitors.

## **7. Conclusions**

The following conclusions have been drawn from this research;

## **Author details**

**Figure 15.** Tafel polarization curves for aluminum alloy in 0.5 M H2

concentrations of FG and ZG at 28°C [46].

*6.3.2. Surfaces analyses (aluminum alloy)*

**S/N C (% g/v) Icorr (A/cm2**

SO4

polarization methods. The data computed for the %IE using linear polarization resistance (LPR), potentiodynamic polarization-corrosion rate (PP-CR), potentiodynamic polarization-corrosion current density (PP-icorr) and weight loss method (WLM) are presented in the Figures above at different concentrations of inhibitors studied. From the given graphs, it is evident that obtained data from the different methods are in good correlation at all the concentrations of inhibitors studied.

**) βc (V/dec) βa (V/dec) LPR**

174 Aluminium Alloys – Recent Trends in Processing, Characterization, Mechanical behavior and Applications

 0.0 1.73E-05 0.025551 0.124930 5.33E+02 0.33054 0.559600 0.5 4.29E-06 0.033853 0.025551 1.47E+03 0.33054 0.138900 1.0 2.71E-06 0.020610 0.059142 2.45E+03 0.11486 0.087732 1.5 6.30E-09 0.892180 1.727600 4.06E+07 0.34318 0.000206 2.0 2.57E-07 0.043434 0.263020 6.30E+04 0.99295 0.008324

**Table 4.** Polarization data for FG and ZG inhibited aluminum alloy in 0.5 M H2

**Rp (Ωcm<sup>2</sup> )**

SO4

solution.

**−Ecorr (V) CR (mm/yr)**

From the SEM/EDS micrographs, aluminum alloy in acidic medium was observed to be more corrosive than aluminum alloy in sodium chloride medium after the immersion tests in both environments in the absence of inhibitors. Significant difference in the morphology of the as-received and the corroded samples of aluminum alloy in the absence and presence of inhibitors revealed that the inhibitors was able to hinder the dissolution of aluminum alloy in all the environments investigated. More uniform films were observed on the surfaces of

medium in the absence and presence of different

Omotayo Sanni\* and Abimbola Patricia Popoola

\*Address all correspondence to<EMAIL_ADDRESS>
Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of Technology, Pretoria, South Africa

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**Chapter 10**

Provisional chapter

**Influence of Rapid Solidification on the**

**Additive Manufactured Ti-6Al-4V Alloy**

Olawale Samuel Fatoba, Esther Titilayo Akinlabi and

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

Mamookho Elizabeth Makhatha

Mamookho Elizabeth Makhatha

Ti-6Al-4V Alloy

Olawale Samuel Fatoba, Esther Titilayo Akinlabi and

Abstract

http://dx.doi.org/10.5772/intechopen.71697

laser, additive manufacturing

1. Introduction

**Thermophysical and Fatigue Properties of Laser**

Influence of Rapid Solidification on the Thermophysical

DOI: 10.5772/intechopen.71697

and Fatigue Properties of Laser Additive Manufactured

Modern industrial applications require materials with special surface properties such as high hardness, wear and corrosion resistance. The performance of material surface under wear and corrosion environments cannot be fulfilled by the conventional surface modifications and coatings. Therefore, different industrial sectors need an alternative technique for enhanced surface properties. The purpose of this is to change or enhance inherent properties of the materials to create new products or improve on existing ones. The most effective and economical engineering solution to prevent or minimize such surface region of a component is done by fiber lasers. Additive manufacturing (AM) is a breaking edge fabrication technique with the possibility of changing the perception of design and manufacturing as a whole. It is well suitable for the building and repairing applications in the aerospace industry which usually requires high level of accuracy and customization of parts which usually employ materials known to pose difficulties in fabrication such as titanium alloys. The current development focus of AM is to produce complex shaped functional metallic components, including metals, alloys and metal matrix composites (MMCs), to meet

demanding requirements from aerospace, defense, and automotive industries.

Keywords: DLMD, solidification, fatigue, wear, Ti-6Al-4V alloy, microstructure, fiber

Titanium is the ninth most abundant element on earth. It occurs as ilmenite, rutile and also present in titanates and iron ores. Titanium and its alloys are preferred choices for chemical, power generation, automobile, aerospace and airframe industries due to their excellent properties.

> © The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **Influence of Rapid Solidification on the Thermophysical and Fatigue Properties of Laser Additive Manufactured Ti-6Al-4V Alloy** Influence of Rapid Solidification on the Thermophysical and Fatigue Properties of Laser Additive Manufactured Ti-6Al-4V Alloy

DOI: 10.5772/intechopen.71697

Olawale Samuel Fatoba, Esther Titilayo Akinlabi and Mamookho Elizabeth Makhatha Olawale Samuel Fatoba, Esther Titilayo Akinlabi and

Additional information is available at the end of the chapter Mamookho Elizabeth Makhatha

http://dx.doi.org/10.5772/intechopen.71697 Additional information is available at the end of the chapter

#### Abstract

Modern industrial applications require materials with special surface properties such as high hardness, wear and corrosion resistance. The performance of material surface under wear and corrosion environments cannot be fulfilled by the conventional surface modifications and coatings. Therefore, different industrial sectors need an alternative technique for enhanced surface properties. The purpose of this is to change or enhance inherent properties of the materials to create new products or improve on existing ones. The most effective and economical engineering solution to prevent or minimize such surface region of a component is done by fiber lasers. Additive manufacturing (AM) is a breaking edge fabrication technique with the possibility of changing the perception of design and manufacturing as a whole. It is well suitable for the building and repairing applications in the aerospace industry which usually requires high level of accuracy and customization of parts which usually employ materials known to pose difficulties in fabrication such as titanium alloys. The current development focus of AM is to produce complex shaped functional metallic components, including metals, alloys and metal matrix composites (MMCs), to meet demanding requirements from aerospace, defense, and automotive industries.

Keywords: DLMD, solidification, fatigue, wear, Ti-6Al-4V alloy, microstructure, fiber laser, additive manufacturing

## 1. Introduction

Titanium is the ninth most abundant element on earth. It occurs as ilmenite, rutile and also present in titanates and iron ores. Titanium and its alloys are preferred choices for chemical, power generation, automobile, aerospace and airframe industries due to their excellent properties.

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

Titanium has high strength and low density (40% lower than steel). Titanium has many alloys with good properties. The most commonly used titanium alloy is the Ti-6Al-4V. It is also known as a workhorse. It is an alpha-beta alloy. Among other properties it possesses is that this alloy is heat treatable and has good hot forming qualities. However, its creep strength is not as good as the alpha alloys. Titanium and its alloys have low density, excellent combination of high specific ratio which is maintained at elevated temperatures, low modulus of elasticity and good corrosion resistance. Biocompatibility of the titanium alloy is excellent and makes it very good for biomedical applications due to its mechanical and corrosion properties. Titanium has a tenacious oxide which forms instantly upon exposure to air. This is the reason for its excellent corrosion resistance [1]. Titanium and it alloys are material of choice in a wide range of industrial applications owing to high strength-to-weight ratio, exceptional biocompatibility and corrosion resistance. However, the use of these materials is compromised due to high fabrication costs which are attributed to difficulty in the machining and loss of material during processing [2]. Estimate by research states that up to 50% of titanium cost are attributed to machining operations [3]. Fortunately, titanium is among the few privileged metallic materials that are fabricated by means of additive manufacturing which has the ability to fabricate high-quality parts with very little or no postmachining [4].

beam focused onto a metallic substrate to generate a molten pool to which a stream of powder is fed. This way, the material volume increases leading to the formation of a solid layer. The laser beam and powder nozzle are repeatedly scanned to accomplish a layered buildup of a solid part by additive manufacturing (AM). The key process parameters are laser power, scan speed, laser beam diameter, and powder feed rate. The parameters influence the thermal phenomena during the growth process of the solid part as well as the metallurgical and mechanical properties. This research will also describe the 2D & 3D multi-physics models to describe the physical mechanism of heat transfer, melting and solidification that take place during and post laser-powder interaction. The transient temperature, geometrical features of the generated structures and thermal cycles will be simulated. The transient temperature is critically important for determining the thermal stress distribution and residual stress state in additively manufactured parts. According to Patterson et al. [8], thermal history generated by a laser beam during additive manufacturing governs the microstructure, properties, residual stress and distortion in fabricated components. In an attempt to overcome or reduce the evolution of residual stresses and the resultant of their unwanted artifacts, modeling and simulation of the additive manufacturing processes is a way to go instead of the time intensive and economic demanding trial and error methods. Additive manufacturing is a process which employs laser radiation to join materials layer by layer to make objects from 3D model data, which is reverse of subtractive manufacturing method. Hanzl et al. [9] stated that different fabrication techniques even when producing components from similar materials result in different properties. Authors further stated that additive manufacturing produces finer grains compared to conventional processes; this is attributed to rapid solidification which is a result of rapid heat conduction from the localized molten zone in direction of the dispersed cool surroundings. Furthermore, additive fabrication provides various benefits including elimination of forming equipment, high material use efficiency and the flexibility of producing customized parts which require very little or no post process machining which makes a direct contribution to the reduction

Influence of Rapid Solidification on the Thermophysical and Fatigue Properties of Laser Additive Manufactured...

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The past decade has seen a rapid development in the range of techniques which are available to modify the surfaces of engineering components. This in turn has led to the emergence of the new field of surface modification. It describes the interdisciplinary activities aimed at tailoring the surface properties of engineering materials. An engineering material usually fails when its surface cannot effectively withstand the external forces or environment to which it is subjected. Serviceable engineering components not only rely on their bulk material properties but also on the design and characteristics of their surface. The surface of these components may require treatment, to enhance the surface characteristics. Surface treatments that cause microstructural changes in the bulk material include heating and cooling/quenching through induction, flame, laser, and electron beam techniques, or mechanical treatments [12]. The behavior of a material is therefore greatly dependent on the surface of a material, surface contact area and the environment under which the material must operate. Surface engineering can cause physical and chemical effects on the bulk material, some beneficial and some detrimental. For example, stresses which may exist in the protective material can create problems; however careful monitoring and research may limit these effects, to hopefully produce quality and serviceable

of production cost and delivery time [10] (Figure 1).

engineering components.

The application of laser surface modification to prolong the service life of engineering components exposed to aggressive environments has gained increasing acceptance in recent years and material processing by laser beams has been well established as an advanced manufacturing technology. The main mandate is the ability to precisely deposit a large amount of energy into a material over a short time range and in a spatially confined region near the surface. One of the major advantages of the laser as a tool for material processing is the ability to precisely control where in the material and at what rate energy is deposited. This control is exercised through the proper selection of laser processing parameters to achieve the desired material modification. Well known applications include the improvement of the wear resistance of diesel engine exhaust valves, the enhancement of the corrosion resistance of gas turbine blades and the repair of dies and inserts. The high-quality surface layers that can be produced by fiber laser only, make it a strategic technique. Surface engineering techniques especially by lasers are known to be cost-effective due to their precision and speed.

Material engineers continue to develop new and existing fabrication techniques in pursuit of improving or entirely replacing the conventional energy intensive, environmentally unfriendly and expensive methods [5]. Metal-based components are generally manufactured by subtractive and formative techniques; with the most recent additive fabrication which has been extensively explored since its development in the late 1980s [6]. The latter widens the perspective and boundaries of design as it provides new possibilities of fabricating complex geometries which are usually unattainable by traditional methods [7].

## 2. Direct laser metal deposition

The direct laser metal deposition (DLMD) is a recently developed technique for manufacturing solid parts, layer by layer, directly from powder. The process uses a high-power laser Titanium has high strength and low density (40% lower than steel). Titanium has many alloys with good properties. The most commonly used titanium alloy is the Ti-6Al-4V. It is also known as a workhorse. It is an alpha-beta alloy. Among other properties it possesses is that this alloy is heat treatable and has good hot forming qualities. However, its creep strength is not as good as the alpha alloys. Titanium and its alloys have low density, excellent combination of high specific ratio which is maintained at elevated temperatures, low modulus of elasticity and good corrosion resistance. Biocompatibility of the titanium alloy is excellent and makes it very good for biomedical applications due to its mechanical and corrosion properties. Titanium has a tenacious oxide which forms instantly upon exposure to air. This is the reason for its excellent corrosion resistance [1]. Titanium and it alloys are material of choice in a wide range of industrial applications owing to high strength-to-weight ratio, exceptional biocompatibility and corrosion resistance. However, the use of these materials is compromised due to high fabrication costs which are attributed to difficulty in the machining and loss of material during processing [2]. Estimate by research states that up to 50% of titanium cost are attributed to machining operations [3]. Fortunately, titanium is among the few privileged metallic materials that are fabricated by means of additive manufacturing which has the ability to fabricate high-quality parts with very little or no post-

182 Aluminium Alloys – Recent Trends in Processing, Characterization, Mechanical behavior and Applications

The application of laser surface modification to prolong the service life of engineering components exposed to aggressive environments has gained increasing acceptance in recent years and material processing by laser beams has been well established as an advanced manufacturing technology. The main mandate is the ability to precisely deposit a large amount of energy into a material over a short time range and in a spatially confined region near the surface. One of the major advantages of the laser as a tool for material processing is the ability to precisely control where in the material and at what rate energy is deposited. This control is exercised through the proper selection of laser processing parameters to achieve the desired material modification. Well known applications include the improvement of the wear resistance of diesel engine exhaust valves, the enhancement of the corrosion resistance of gas turbine blades and the repair of dies and inserts. The high-quality surface layers that can be produced by fiber laser only, make it a strategic technique. Surface engineering techniques especially by lasers are

Material engineers continue to develop new and existing fabrication techniques in pursuit of improving or entirely replacing the conventional energy intensive, environmentally unfriendly and expensive methods [5]. Metal-based components are generally manufactured by subtractive and formative techniques; with the most recent additive fabrication which has been extensively explored since its development in the late 1980s [6]. The latter widens the perspective and boundaries of design as it provides new possibilities of fabricating complex geome-

The direct laser metal deposition (DLMD) is a recently developed technique for manufacturing solid parts, layer by layer, directly from powder. The process uses a high-power laser

known to be cost-effective due to their precision and speed.

tries which are usually unattainable by traditional methods [7].

2. Direct laser metal deposition

machining [4].

beam focused onto a metallic substrate to generate a molten pool to which a stream of powder is fed. This way, the material volume increases leading to the formation of a solid layer. The laser beam and powder nozzle are repeatedly scanned to accomplish a layered buildup of a solid part by additive manufacturing (AM). The key process parameters are laser power, scan speed, laser beam diameter, and powder feed rate. The parameters influence the thermal phenomena during the growth process of the solid part as well as the metallurgical and mechanical properties. This research will also describe the 2D & 3D multi-physics models to describe the physical mechanism of heat transfer, melting and solidification that take place during and post laser-powder interaction. The transient temperature, geometrical features of the generated structures and thermal cycles will be simulated. The transient temperature is critically important for determining the thermal stress distribution and residual stress state in additively manufactured parts. According to Patterson et al. [8], thermal history generated by a laser beam during additive manufacturing governs the microstructure, properties, residual stress and distortion in fabricated components. In an attempt to overcome or reduce the evolution of residual stresses and the resultant of their unwanted artifacts, modeling and simulation of the additive manufacturing processes is a way to go instead of the time intensive and economic demanding trial and error methods. Additive manufacturing is a process which employs laser radiation to join materials layer by layer to make objects from 3D model data, which is reverse of subtractive manufacturing method. Hanzl et al. [9] stated that different fabrication techniques even when producing components from similar materials result in different properties. Authors further stated that additive manufacturing produces finer grains compared to conventional processes; this is attributed to rapid solidification which is a result of rapid heat conduction from the localized molten zone in direction of the dispersed cool surroundings. Furthermore, additive fabrication provides various benefits including elimination of forming equipment, high material use efficiency and the flexibility of producing customized parts which require very little or no post process machining which makes a direct contribution to the reduction of production cost and delivery time [10] (Figure 1).

The past decade has seen a rapid development in the range of techniques which are available to modify the surfaces of engineering components. This in turn has led to the emergence of the new field of surface modification. It describes the interdisciplinary activities aimed at tailoring the surface properties of engineering materials. An engineering material usually fails when its surface cannot effectively withstand the external forces or environment to which it is subjected. Serviceable engineering components not only rely on their bulk material properties but also on the design and characteristics of their surface. The surface of these components may require treatment, to enhance the surface characteristics. Surface treatments that cause microstructural changes in the bulk material include heating and cooling/quenching through induction, flame, laser, and electron beam techniques, or mechanical treatments [12]. The behavior of a material is therefore greatly dependent on the surface of a material, surface contact area and the environment under which the material must operate. Surface engineering can cause physical and chemical effects on the bulk material, some beneficial and some detrimental. For example, stresses which may exist in the protective material can create problems; however careful monitoring and research may limit these effects, to hopefully produce quality and serviceable engineering components.

a reliable coating that is free of cracks and pores can be produced on the matrix. LSA can rapidly provide a thick and crack-free layer in all instances with metallurgical bonds at the interface between the alloyed layer and the substrate [19]. In LSA, external alloying elements in form of powder (metal, alloy, ceramic, cermet or intermetallic) are introduced into the surface of a substrate, as pre-placed material or injected directly into the melt pool created on the substrate by a high-power laser beam. The melting of the substrate occurs rapidly only at the

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The result of this is rapid self-quenching and resolidification of new alloy due to the large temperature gradients between the melted surface region and the underlying solid substrate. The evolution of a wide variety of microstructures as a result of the rapid cooling from the liquid phase is one of the consequences [20]. Hence, during laser alloying process, the synthesis of new alloy is possible by depositing a premixed ratio of elemental powders. Powders surfaced on new or worn working surfaces of components by LSA provides specific properties such as high abrasive wear resistance, erosion resistance, corrosion resistance, heat resistance and combinations of these properties. Consequently, improvements in machinery performance and safety in aerospace, automotive, can be realized by the method [21]. According to Poulon-Quintin et al. [22], laser beams, because of specific thermal characteristics induced by laser irradiation, can generate specific microstructures including metastable phases and nano-crystalline grains. Laser processing offers unique and significant quality and cost advantages over traditional techniques. These include high throughput speed, process compatibility, high process efficiency, low porosity and good surface uniformity. In addition, the rapid self-quenching in laser alloying results in a true metallurgical bond between the composite layer and the substrate, the formation of a nonequilibrium or amorphous phase as well as homogenization and refinement of the microstructure,

3. Overview on application and improved properties of laser deposited

Xu et al. [26] investigated additive manufacturing ductile and strong Ti6Al4V by using selective laser melting through in situ martensite decomposition. Ti6Al4V powder was used to fabricate cubes and cylindrical bars by using a selective laser melting (SLM) facility with different process parameters. Different layer thicknesses were applied, 30, 60 and 90 μm and the process was carried out in an argon atmosphere. The samples were then subjected to isothermal treatment for 2 hours at temperatures ranging from 350 to 930�C. The tensile strength of the samples was evaluated and compared to Ti6Al4V manufactured by mill annealing and by solution treating and aging (STA). The microstructural analysis was completed by means of SEM and phase examination was carried out by X-ray diffraction. The results should that the finest columnar prior β grains were found in the 30 μm thick layer in comparison to the 60 and 90 μm thicknesses; this was attributed to fast cooling condition. It was found that a smaller focal offset distance (0–2 mm) resulted in an ultrafine lamellar (α + β) microstructure, whereas a focal offset distance of 4 mm led to an acicular α<sup>0</sup> martensitic microstructure. This led to the authors concluding that the transformation of martensite to

surface, while the bulk of the material remains cool, thus serving as an infinite heat sink.

all without affecting the bulk properties of the substrate [23�25].

and additive manufactured Ti-6Al-4V alloy

Figure 1. Schematic diagram illustrating the heat affected zone and melt zone created by laser surface melting [11].

The choice of a surface material with the appropriate thermal and sufficient resistance to wear and corrosion degradation is crucial to its functionality. The desired properties of surfaceengineered components are improved corrosion resistance through barrier or sacrificial protection, improved wear resistance and mechanical properties such as fatigue and toughness. The surface modification of metals, using high intensity lasers, accepts various methods in making use of the heat from the laser beam in enhancing the morphology and microstructure in order to achieve numerous metallurgical outcomes [13]. Laser surface modification of materials entails an extensive composition of additive and subtractive methods. Metals such as magnesium, titanium and aluminum blend extremely desired properties with light weight without a significant alteration of the bulk material. This is the footing for high demand of laser surface modification techniques [14]. There are many laser surface treatment techniques responsible for fabrication of highly corrosion-resistant metallic surfaces, where the major ones used are laser surface melting, laser cladding and laser surface alloying [15, 16].

Laser surface alloying (LSA) modifies the surface morphology and near surface structure of components and its alloys with perfect adhesion to the interface of the bulk steel. The distinctive advantages of the LSA technique for surface modification include the refinement of the grain size because of rapid quench rates and the generation of meta-stable structures with novel properties that are not feasible by competing methods [17, 18]. With optimum laser processing parameters, a reliable coating that is free of cracks and pores can be produced on the matrix. LSA can rapidly provide a thick and crack-free layer in all instances with metallurgical bonds at the interface between the alloyed layer and the substrate [19]. In LSA, external alloying elements in form of powder (metal, alloy, ceramic, cermet or intermetallic) are introduced into the surface of a substrate, as pre-placed material or injected directly into the melt pool created on the substrate by a high-power laser beam. The melting of the substrate occurs rapidly only at the surface, while the bulk of the material remains cool, thus serving as an infinite heat sink.

The result of this is rapid self-quenching and resolidification of new alloy due to the large temperature gradients between the melted surface region and the underlying solid substrate. The evolution of a wide variety of microstructures as a result of the rapid cooling from the liquid phase is one of the consequences [20]. Hence, during laser alloying process, the synthesis of new alloy is possible by depositing a premixed ratio of elemental powders. Powders surfaced on new or worn working surfaces of components by LSA provides specific properties such as high abrasive wear resistance, erosion resistance, corrosion resistance, heat resistance and combinations of these properties. Consequently, improvements in machinery performance and safety in aerospace, automotive, can be realized by the method [21]. According to Poulon-Quintin et al. [22], laser beams, because of specific thermal characteristics induced by laser irradiation, can generate specific microstructures including metastable phases and nano-crystalline grains. Laser processing offers unique and significant quality and cost advantages over traditional techniques. These include high throughput speed, process compatibility, high process efficiency, low porosity and good surface uniformity. In addition, the rapid self-quenching in laser alloying results in a true metallurgical bond between the composite layer and the substrate, the formation of a nonequilibrium or amorphous phase as well as homogenization and refinement of the microstructure, all without affecting the bulk properties of the substrate [23�25].

## 3. Overview on application and improved properties of laser deposited and additive manufactured Ti-6Al-4V alloy

The choice of a surface material with the appropriate thermal and sufficient resistance to wear and corrosion degradation is crucial to its functionality. The desired properties of surfaceengineered components are improved corrosion resistance through barrier or sacrificial protection, improved wear resistance and mechanical properties such as fatigue and toughness. The surface modification of metals, using high intensity lasers, accepts various methods in making use of the heat from the laser beam in enhancing the morphology and microstructure in order to achieve numerous metallurgical outcomes [13]. Laser surface modification of materials entails an extensive composition of additive and subtractive methods. Metals such as magnesium, titanium and aluminum blend extremely desired properties with light weight without a significant alteration of the bulk material. This is the footing for high demand of laser surface modification techniques [14]. There are many laser surface treatment techniques responsible for fabrication of highly corrosion-resistant metallic surfaces, where the major ones

Figure 1. Schematic diagram illustrating the heat affected zone and melt zone created by laser surface melting [11].

184 Aluminium Alloys – Recent Trends in Processing, Characterization, Mechanical behavior and Applications

used are laser surface melting, laser cladding and laser surface alloying [15, 16].

Laser surface alloying (LSA) modifies the surface morphology and near surface structure of components and its alloys with perfect adhesion to the interface of the bulk steel. The distinctive advantages of the LSA technique for surface modification include the refinement of the grain size because of rapid quench rates and the generation of meta-stable structures with novel properties that are not feasible by competing methods [17, 18]. With optimum laser processing parameters, Xu et al. [26] investigated additive manufacturing ductile and strong Ti6Al4V by using selective laser melting through in situ martensite decomposition. Ti6Al4V powder was used to fabricate cubes and cylindrical bars by using a selective laser melting (SLM) facility with different process parameters. Different layer thicknesses were applied, 30, 60 and 90 μm and the process was carried out in an argon atmosphere. The samples were then subjected to isothermal treatment for 2 hours at temperatures ranging from 350 to 930�C. The tensile strength of the samples was evaluated and compared to Ti6Al4V manufactured by mill annealing and by solution treating and aging (STA). The microstructural analysis was completed by means of SEM and phase examination was carried out by X-ray diffraction. The results should that the finest columnar prior β grains were found in the 30 μm thick layer in comparison to the 60 and 90 μm thicknesses; this was attributed to fast cooling condition. It was found that a smaller focal offset distance (0–2 mm) resulted in an ultrafine lamellar (α + β) microstructure, whereas a focal offset distance of 4 mm led to an acicular α<sup>0</sup> martensitic microstructure. This led to the authors concluding that the transformation of martensite to ultrafine lamellar structure is possible by manipulating the process parameters of selective laser melting. The high yield strength and elongation failure of the SLM fabricated Ti6Al4V with ultrafine lamellar is comparable with STA Ti6Al4V and was better than that of millannealed Ti6Al4V, with results of >1100 MPa yield strength and 11.4% failure elongation. The heat treatment of the samples revealed that decomposition of α<sup>0</sup> martensite into ultrafine lamellar took place from 400�C. It was therefore concluded by the authors that additive manufacturing of Ti6Al4V by SLM can improve the properties.

HV0.5 to 342 HV0.5. The samples subjected to heating to 1200C for 2 hours and then cooled in a furnace had a lower hardness of 308 HV0.5 due to change of the initial morphology to equiaxed

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Makuch et al. [29] studied the laser surface alloying of commercially pure titanium using carbon and boron. The use of titanium alloys ranges over many industries but the application in friction and wear conditions is limited due to their high tendency to adhesive wear, poor hardness and low wear resistance. Thermo-chemical processes such as boriding, nitriding and carburizing have been applied to steels and Ti alloys in order to improve the wear performance, but the disadvantages are that the thermal diffusion process requires high temperatures to achieve an acceptable layer thickness and the duration of the process is long. The material to be laser surface alloyed with boron and carbon was ring-shaped commercially pure titanium Grade 2. Three different pastes were produced for alloying; boron, boron and carbon, and carbon were mixed with polyvinyl alcohol to produce the pastes. The external surface of the cylinders was coated by the three different pastes and then the surface was re-melted with a continuous-wave CO2 laser. OPM and SEM were used to analyze the microstructure, XRD was used to examine the phases present, a Vickers hardness tester was used to determine the microhardness and a frictional pair was used to evaluate the abrasive wear of the layers. The greatest microhardness was achieved by the borided and borocarburized layers with 1250–1650 HV and 1200–1750 HV respectively, a hardness of 1000–1500 HV was obtained for the carburized layer. The increase in hardness was attributed to the formation of hard ceramic phases; TiB, TiB2 and TiC. It was found that of the coatings, the borocarburized layer exhibited the worst wear and friction performance and the laser borided sample had the best friction behavior and the laser-carburized had the best wear performance. It was concluded by the authors that laser alloying with boron and

Yang et al. [30] investigated synthesizing, microhardness and microstructure distribution of Ti-Si-C-N/TiCN composite coating fabricated on Ti6Al4V by laser cladding. TiN and TiCN coatings have been broadly used to extend the lifetime of medical and cutting tools due to their high hardness, good wear performance, biocompatibility, excellent corrosion resistance and affordable price. Although the properties of TiCN coatings are desirable, their thermal stability is not adequate and can be improved by adding SiO2 to the coating. A combination of titanium carbonitride and silica powders (20% SiO2) was used to coat Ti6Al4V alloy by means of a YAG laser system. The laser beam scanning speed was varied at 1, 2, 3 and 4 mm/s in order to examine how the properties will be affected. XRD was used to analyze the phases, SEM-EDS was used to characterize the microstructure and a microhardness tester with a load of 200 g and a dwelling time of 10 s was used to measure the microhardness. The phases that were obtained were TiC0.3N0.7, Ti3SiC2 and Ti2O. As the scan speed increased, the relative amount of TiC0.3N0.7 decreased, amounts Ti3SiC2 increased by more than two times at a speed of 2 mm/s from a speed of 1 mm/s and increased gradually after that, and the amount of Ti2O was low at 1 mm/s, increased sharply at 2 mm/s and then decreased by almost half for the following speeds. The microhardness of the coatings increased from 1005 HV at 1 mm/s to 1400 HV at 3 mm/s was reached, for 4 mm/s, the hardness reduced. The authors therefore concluded that

laser cladding Ti6Al4V at 3 mm/s will produced the most desired properties.

carbon will improve the wear resistance of titanium alloys.

prior β grains.