Glossary of Terms



AAMA Abbreviation for American Architectural Manufacturers Association.
AEC Abbreviation for Aluminum Extruders Council.
AMS Abbreviation for Aerospace Material Specification.
ANSI Abbreviation for American National Standards Institute.
ASCA Abbreviation for Architectural Spray Coaters Association.
ASD Abbreviation for Aluminum Standards and Data, published by the Aluminum Assoc.
ASME Abbreviation for American Society of Mechanical Engineers.
ASTM Abbreviation for American Society for Testing and Materials.
AGE HARDENING An aging process that results in increased strength and hardness.
AGE SOFTENING Spontaneous decrease of strength and hardness that takes place at room temperature in certain strain hardened alloys containing magnesium.
ALODIZING (not to be confused with anodizing, a different process). Applies to use of an Amchem Products solution known as Alodine, one of several types of conversion coatings used in extruded sign panels and heat sinks, etc.
ALUMINA Aluminum oxide produced from bauxite by chemical reduction. It is a white powdery material that looks like granulated sugar. Alumina is an intermediate step in the production of aluminum from bauxite, and is also a valuable chemical on its own.
ALUMINUM A silver-white soft metal, noted for its lightness, high reflectivity, high thermal conductivity, non-toxicity, and corrosion resistance. It is the most abundant metallic element, comprising about 1/12th of the earth’s crust. It is never found in nature as an elemental metal, but only in combination with oxygen and other elements. In ordinary commercial and industrial use, the work “aluminum” is often understood to mean aluminum alloy, rather than the pure metal.
ANGULARITY Conformity to, or deviation from, specified angular dimensions in the cross-section of a shape or bar.
ANODIZING Forming a coating on a metal surface produced by electrochemical treatment through anodic oxidation. This process may be used to increase the protective effect of aluminum’s transparent natural oxide surface. It may also be given a decorative coloration.
APERTURE In an extrusion die, the shaped opening through which the heat-softened metal is forced and which gives the extruded product its cross-sectional shape. Also called the “orifice”.
AS-CAST The metallurgical structure characteristic of aluminum ingot which has not been worked. It is non-homogeneous in that alloying constituents are rich in some areas and scarce in others.
ASSEMBLY FIT Refers to two parts designed for mating assembly and requiring exact dimensions and contours to assure a proper fit.
Back to top


BACKER (back-up plate) A ‘tool’, or reinforcing part, which presses against the outer surface of an extrusion die, supporting it against the pressure of the extruding metal. The backer has an opening larger than the die aperture, allowing the extruded product to emerge without marring its soft surface.
BACK TAPER (Relief) Cut-away portion of die beginning at breakaway point to the die exit either angled or undercut (stepped back) for back clearance.
BAR A solid extrusion that is long in relation to cross-section, which is square or rectangular (excluding plate or flattened wire) with sharp or rounded corners or edges; or is a regular hexagon or octagon; and in which at least one perpendicular distance between parallel faces is 0.375 inch or greater. (Smaller sizes are classified as wire).
BASE METAL (1) The metal present in the largest proportion in an alloy; (2) the metal to be brazed, cut or welded; (3) after welding, the part of the metal that was not melted during the process.
BEARING The surface of the extruding aperture, at right angles to the die face, that controls metal flow and to some extent speed of flow which is also the conforming surface along which aluminum flows.
BEND RADIUS This rule-of-thumb measurement describes a material’s ability to bend to a 90 degree inside angle with the use of a “vee” press brake die. Bend radius charts provide recommended minimum inside bend radii, showing how sharp a bend can be made in metal without fracturing it on the outside of the bend. Considering a metal’s mechanical properties and thickness, one should fabricate an inside.
BILLET, CONTAINER The part of an extrusion press into which the billet to be extruded is placed.
BILLET, EXTRUSION May be solid or hollow in form, commonly cylindrical, used as the final length of material charged into the extrusion press cylinder. It is usually a cast product, but may be wrought product or sintered from powder compact.
BLANK A piece of metal cut or formed to regular or irregular shape for subsequent processing such as by forming, bending, or drawing. The piece of sheet stock cut out by blanking die. It will subsequently by drawn into a cup or end shell.
BLISTERING A defect in the paint film appearing as “bubbles”, usually caused by the expansion of air, solvent vapor, or moisture trapped beneath the film.
BLOOM A semi-finished hot rolled product, rectangular or square in cross section, produced on a blooming mill.
BOLSTER A “tool”, or reinforcing part, which supports the (die block) backer – which in turn, supports an extruding die against the pressure of extrusion.
BOW Longitudinal curvature of rod, bar, profiles (shapes), and tube. Bow is measured after allowing the weight of the extrusion to minimize the deviation. Bow can be caused by a non-uniform extrusion rate across the cross-section resulting in one portion of the extrusion being longer than the other or non-uniform contraction during quenching.
BOW, LATERAL Deviation from straight of a longitudinal edge.
BOW, LONGITUDINAL Curvature in the case of sheet or plate in the rolling direction, along the length of an extrusion.
BOW, TRANSVERSE Curvature across the rolling direction of sheet or plate, across the width of an extrusion.
BRIDGE In extrusion: the part of an extrusion “bridge die” that supports a void-forming mandrel. During extrusion, the metal divides and flows around the bridge, reuniting as it is extruded through the die orifice. The resulting weld line can be detected upon microscopic examination, but the extrusion appears functionally and visually seamless.
BRIDGE TYPE DIE A die having a stationary core or mandrel which is held in place by core supports or webs (bridge) bolted to the back of the die. The die contains a weld chamber so that when the billet is pushed the metal divides to flow around the core supports and welds together in the welding chamber before passing through the die. See “Die, Porthole”. Bridge normally have unenclosed ports which protrude into the container liner.
BRIGHT DIPPING Chemical polishing of Aluminum, often by treatment with a mixture of nitric acid and phosphoric acid, yielding a mirror-shiny (specular), highly reflective surface. It is almost always followed by anodizing to protect the surface and provide some choice colors.
BRINELL HARDNESS TEST See “Hardness, Brinell”.
BUCKLE A distortion of the surface of the material.
BUS BAR OR BUS CONDUCTOR A metal bar for conducting a heavy flow of electric current.
BUTT The unextruded portion of the billet remaining in the container after the extrusion cycle is completed. The butt varies in thickness depending upon the alloy, die configuration, and extruded profile characteristics.
Back to top


CAD Computer Assisted Design. The use of computer programs to generate, analyze, and modify designs. Extrusion dies and their supporting tools, for example, may be with the aid of computers.
CAM Computer Assisted Manufacturing. The use of computers to monitor, regulate, and control manufacturing processes.
CAP The outer part of a hollow die, which shapes the outside of a hollow extrusion.
CAUSTIC ETCH A pretreatment for anodizing. Bare, clean aluminum is subjected to a caustic bath, producing a soft matte, or frosted, appearance which is more attractive under transparent anodic film.
CAST To form a molten material into a desired shape by pouring into a mold and letting it harden.
CHATTER MARK Numerous intermittent lines or grooves that are usually full width and perpendicular to the extrusion direction.
CIRCUMSCRIBING CIRCLE The smallest circle that will completely enclose the cross section of an extruded shape.
CLASS I-HOLLOW SHAPE Hollow extruded shapes whose void is round and one inch or more in diameter, and whose weight is equally distributed.
CLASS II-HOLLOW SHAPE Any hollow extruded shape other than Class I, which does not exceed a 5-inch diameter circumscribing circle and has a single void of not less than .375-inch diameter of .110 square inch area. The inside contour of the profile being extruded. After flowing around the supports, the metal is fused in a weld chamber before passing through the die (die cap) proper.
CLASS III-HOLLOW SHAPE Any hollow extruded shape other than Class I or Class II.
BOW, LATERAL Deviation from straight of a longitudinal edge.
CONDUCTIVITY The ability of a substance to transmit heat, light or electricity. Aluminum has high electrical and thermal conductivity, making it useful in a wide range of electrical and heat-exchanging applications.
CONTAINER The steel cylinder, usually fitted with a removable liner, having an inside diameter slightly larger than the billet to be extruded which holds and confines the billet during the extrusion cycle. Its length may vary with the press tonnage rating and manufacturer.
CORROSION The deterioration of metal by chemical or electrochemical reactions with substances in its environment.
CORROSION, PITTING Localized corrosion resulting in small pits or craters in a metal surface.
CORROSION, WATER STAIN Superficial oxidation of the water surface with a water film, in the absence of circulating air, help between closely adjacent metal surfaces.
COUPON A piece of metal from which a test specimen may be prepared.
Back to top


DIE ASSEMBLY In an extrusion press, the die and its associated tooling.
DIE FACE The surface of an extrusion die facing the billet.
DIE, HOLLOW A steel extrusion tool which forms extruded “closed” profiles containing one or more voids such as rectangular tubing. The tool generally consists of a die cap which generates the outer surface of the profile and the mandrel or core which generates the inside contour. Hollow or semi-hollow profiles are produced usually with either bridge, porthole or spider (taper seal) type dies are variants thereof. Extruded sections produced on such dies have seams or longitudinal weld lines, due to the metal flow around the web supports (bridges) that hold the mandrel.
DIE LINES A longitudinal depression or protrusion formed on the surface of drawn or extruded material. Die lines are preset to some degree in all extrusions and are caused by a roughening of the die bearing.
DIE, PORTHOLE A die having a stationary core or mandrel which is held in place by integral core supports or webs. The porthole die is a modification of the spider die, except that the spider is replaced with a chambered disk that supports the mandrel (sometimes termed a “stub mandrel”); several “portholes” running through it annularly about the mandrel, distinguish the porthole types. The die contains a weld chamber so that when the billet is pushed the metal divides the flow around the core supports and welds together in the welding chamber before passing through the die. Porthole dies are used in producing extruded hollow profiles and tubing. See “Bridge”, and “Bridge Type Die.”
DIE RING A cylindrical sleeve that holds the die and backer in axial relationship to each other.
DIE, SEMI-HOLLOW A circular steel extrusion tool which forms an “open” profile with a high tongue ratio. Generally this tongue ratio is greater than three to one. This type of die is similar to a hollow die. The tongue is protected by a web or bridge which reduces the billet pressure. When possible, for maximum support the tongue should be bolted to the web.
DIE, SOLID A steel disk, with one or more orifices or aperatures, of similar cross-section and contour as the desired product, through which metal is forced forming “open” profiles such as bar, channel, and angle. Such dies are generally employed where profiles other than hollow are required.
Back to top


ETCHING Shaping or texturing a metal surface by controlled corrosive action.
EXPOSED SURFACE Any face of an extruded profile which is exposed to view or other critical end-use aspects.
EXTRUDE To force material through a die by pressure.
EXTRUSION BILLET The starting stock for the extrusion operation. Extrusion billet is a solid or hollow form, commonly cylindrical and is the length charged into the extrusion press cylinder. It is usually a cast product but may be a wrought product or powder compact.
EXTRUSION (direct) The method of extruding wherein the die and ram are at opposite ends of the billet and the product and ram travel in the same direction.
EXTRUSION LOG The starting stock for extrusion billet. Extrusion log is usually produced in lengths from which shorter extrusion billets are cut.
EXTRUSION PRESSURE That force employed to cause billet metal flow through a die.
EXTRUSION SPEED The velocity or rate at which an extrusion exits from the die usually expressed as feet per minute.
Back to top


FEEDER DIE A die design which permits through certain design features the extrusion of profiles normally too large for an extrusion press if conventional means were employed or to assist in extrusion of difficult profiles. (See “Feeder Plate”.)
FEEDER PLATE A tooling component placed in front of the extrusion die to alter the metal billet dimensions. It may be used to permit extrusion of larger dimensioned product than normally possible or to assist in extrusion of difficult profiles by modifying the flow characteristics of the metal.
FILLET Generally, a concave junction where two surfaces meet.
FINISH In extrusion, the condition, quality or appearance of the final aluminum surface. Aluminum can be finished in a very wide variety of textures and colors.
FINISHING Operations to alter a material’s appearance, improve corrosion resistance, improve aesthetics, or prepare for special application. Includes:

  • Applied Finishing-Painting, plating, laminating or porcelainizing.
  • Chemical Finishing (such as caustic etching or bright dipping). Preparation for painting or anodizing with conversion coating.
  • Electrolytic Finishing – Any anodizing process.
  • Mechanical Finishing – Buffing, sanding, grinding, polishing, or blasting with shot or sand.
FLASH A thin protrusion at the parting line of a forging or casting which forms when metal, in excess of that required to fill the impressions, is forced between the die interfaces. Also, metal forced between container and die due to improper seal.
FLATNESS (1) For rolled products, a distortion of the surface of sheet such as a bulge or a wave, usually transverse to the direction of rolling. Often described by location across width, i.e. edge buckle, quarter buckle, center buckle, etc. (2) For extrusions, flatness (off contour) pertains to the deviation of a cross-section surface intended to be flat. Flatness can be affected by conditions such as die performance, thermal effects, and stretching.
Back to top


GAUGE A term previously used in referring to the thickness or diameter of a wrought product. Thickness or diameter is preferred in dimension description.
GRAIN REFINING Adding certain elements, such as titanium, to molten aluminum to reduce the grain size.
GRAIN (1) The direction of the fibers in a material. (Paper and board resist bending against the grain). In a non-fibrous material, the direction of molecular orientation. (2) An individual crystal in metal.
Back to top


HARD COAT ANODIZING A combined electrical and chemical finishing process for Aluminum Anodizing that produces a hard, colored, protective film on the surface.
HARDNESS, BRINELL A measure of hardness (resistance to indentation) obtained by applying a load – through the use of a ball indenter – and measuring the permanent impression in the material. The hardness value of aluminum alloys is obtained by applying a load of 500 kilograms to a ball 10 millimeters in diameter for 30 seconds; the applied load (in kilograms) is divided by the spherical area of the impression (in square millimeters).
HARDNESS, ROCKWELL An indentation hardness test based on the depth of penetration of a specified penetrator into the specimen under certain fixed conditions.
HEAT-AFFECTED ZONE That portion of the base metal in welding, brazing or flame cutting whose microstructure and physical properties have been altered by the heat.
HEAT-TREATABLE ALLOY An aluminum alloy that can be hardened or softened to produce desired properties by a controlled cycle of heating and cooling. Includes 2xxx, 6xxx and 7xxx series.
HEAT TREATING Applying a controlled cycle of heating and cooling to an alloy to produce specific mechanical properties. Certain heat treatments strengthen aluminum alloys, while others make them soft for maximum workability.
HOLLOW BILLET A billet prepared for extruding seamless tube or pipe. The outside diameter may be scalped and the inside diameter may be bored or cast hollow to assure sound metal.
HOLLOW DIES Are extrusion tools capable of forming profiles with voids where such dies are typically classified as either bridge, porthole or spider types. Extruded sections produced on these dies have one or more seams on longitudinal weld lines, due to metal flow around the supports that hold the stub mandrel. The stub mandrel determines the inside contour of the section being extruded. After passing around the supports, the metal is fused in a weld chamber before passing through the die proper.
HOLLOW PROFILE An extruded profile, any part of whose cross-section completely encloses a void.
HOLLOW SHAPE An extruded shape, any part of whose cross-section completely encloses a void.
Back to top


IMPACT A part formed in a confining die from a metal slug, usually cold, by rapid single stroke application of force through a punch, causing the metal to flow around the punch and/or through an opening in the punch or die.
IMPACT STRENGTH The ability of a material to withstand shock loading.
INCLUSION Foreign material in the metal or impressed into the surface.
INCLUSION, STRINGER An impurity, metallic or nonmetallic, which is trapped in the ingot and elongated subsequently in the direction of working. It may be revealed during working or finishing as a narrow streak parallel to the direction of working.
INGOT A mass of cast metal, usually intended for subsequent rolling, extrusion or forging operations. (Includes the obsolete term “pig”.)
Back to top


LAMINATION An internal crack or separation aligned parallel to the extrusion direction, usually caused by contaminants that feed into the flow during the forming process or by cracked billets.
LOT, INSPECTION (1) For non-heat treated tempers, an identifiable quantity of material of the same mill form, alloy, temper, section and size submitted for inspection at one time. (2) For heat treated tempers, and identifiable quantity of material of the same mill form, alloy, temper, section and size traceable to a heat treat lot or lots and submitted for inspection at one time.
Back to top


MACHINABILITY The relative ease of working a metal with machine tools. Aluminum has good machinability.
MANDREL The fixed or floating projection positioned in the die opening that forces metal to flow around it. The wall thickness of the extrusion is determined by the difference in the dimensions of the die aperture and the mandrel.
MARK, BEARING A depression in the extruded surface caused by a change in bearing length in the extrusion die.
MARK, CARBON (graphite) Gray and black surface marking caused by contact with carbon runout blocks.
MARK, CHATTER Numerous intermittent lines or grooves that (roll or leveller) are usually full width and perpendicular to the rolling or extrusion direction.
MARK, SNAP A band-like pattern visible around the full perimeter for an extruded section and perpendicular to its length. A snap mark can occur whenever there is an abrupt change in the extrusion process.
MODULUS OF ELASTICITY The ratio of stress to corresponding strain throughout the range where they are proportional. As there are three kinds of stresses, so there are three kinds of moduli of elasticity for any material – modulus in.
Back to top


NATURAL AGING The process by which certain aluminum alloys continue to improve their mechanical properties at room temperature.
Back to top


OVALITY Deviation from a circular periphery, usually expressed as the total difference found at any one cross-section between the individual maximum and minimum diameters, which usually occur at or about 90 degrees to each other. Since ovality is the difference between extreme diameters, it is not expressed as plus or minus.
Back to top


PICKUP Small particles of oxide adhering to the surface of a product at irregular intervals.
PIPE Tube in standard combinations of outside diameter and wall thickness, commonly designated by “Nominal Pipe Sizes” and “ANSI Schedule Numbers.”
PORTS On the feed area on the entry side of a hollow die, the openings through which the metal stream flows.
PROFILE A product that is long in relation to its cross-sectional dimensions, having a cross-section other that those of wire, rod, bar, and tube, produced by extrusion, rolling, drawing, or cold finishing. Formerly termed a “shape”.
PROFILE, SEMI-HOLLOW A profile any part of whose cross-section is a partially enclosed void the area of which is substantially greater than the square of the width of the gap. The ratio of the area of the void to the square of the gap is dependent on the class of semi-hollow profile, the alloy and the gap width.
PULLER A device which guides metal down the runout table as it is being extruded.
Back to top


QUENCHING Controlled rapid cooling of a metal from an elevated temperature by contact with a liquid, gas or a solid.
Back to top


ROD A solid wrought product, long in relation to its cross-section, which is not less than 0.375 inch in diameter. (Smaller sizes are classified as wire.)
Back to top


SCALPING Removing a surface layer from a cast aluminum ingot or billet to remove impurities and the ascast finish.
SEAMLESS A hollow product which does not contain any line junctures resulting from method of manufacture.
SHIFTING WALLS Uneven walls caused by core (mandrel) movement.
STABILIZING A low temperature thermal treatment designed to prevent age-softening in certain strain hardened alloys containing magnesium.
STAIN, HEAT TREAT A discoloration due to nonuniform oxidation of the metal surface during heat treatment.
STAIN, OIL Surface discoloration which may vary from dark brown to white and is produced during thermal treatment by incomplete evaporation and/or oxidation of lubricants on the surface.
STANDARD TOLERANCE An established dimensional tolerance for a certain class of product. Aluminum extrusions are produced to standard dimensional tolerances as defined in ANSI Standard H35.2 (and reprinted in Aluminum Standards and Data), unless otherwise specified.
STRENGTH/WEIGHT RATIO The relationship between the structural strength of a material and its weight. The strength-to-weight ratio of structural aluminum alloys is about twice that of mild steel.
STRESS RELIEVING The reduction of the effects of internal residual stresses by thermal or mechanical means.
STRETCH STRAIGHTENING The process of stretching extruded sections beyond the yield strength of the alloy to achieve longitudinal straightness.
STRUCTURAL SHAPE An aluminum section, now usually extruded, of any design accepted as standard by the structural industry. Such shapes include I-beams, wide flange of H-beams, channels, angles, tees and zees.
SUB-BOLSTER A hardened alloy steel disk often employed when the bolster does not fill the die stack. See “Bolser”.
Back to top


TEARING Typically cracks or separations due to high extrusion speed or extrusion temperature.
TENSILE STRENGTH In tensile testing, the ratio of maximum load to original cross-sectional area. Also called “Ultimate Strength”.
TOLERANCE Allowable deviation from a nominal or specified dimension.
TONGUE RATIO A method used to define semi-hollow dies/profiles, whereby the area of the partially enclosed void is divided by the square of the gap (Area/Gap^2).
TRANSVERSE WELD A condition existing within an extrusion which is created by the interface of two separate billets. In practice the interface is extruded at different rates through the die and is formed into a conical or pointed configuration within a portion of the extrusion.
TUBE A hollow wrought product that is long in relation to its cross-section, which is symmetrical and is round, a regular hexagon or octagon, elliptical, or square or rectangular with sharp or rounded corners, and that has uniform wall thickness except as affected by corner radii.
TUBE, FLUTED A tube of nominally uniform wall thickness having regular, longitudinal, concave corrugations with sharp cusps between corrugations.
TWIST A winding departure from straightness.
Back to top


ULTIMATE STRENGTH The maximum conventional stress (tensile, compressive or shear) that a material can withstand.
ULTRASONIC TESTING A nondestructive test applied to sound-conductive materials having elastic properties for the purpose of locating inhomogeneities or structural discontinuities within a material by means of an Ultrasonic Beam.
Back to top



WAVING A ripple effect, usually in the leg or legs of an extrusion, caused primarily by either an excessive deflection in the tooling, excessive heat or unbalanced feed.
WIRE A solid wrought product that is long in relation to its cross-section, which is square or rectangular with sharp or rounded corners or edges, or is round, hexagonal, or octagonal, and whose diameter or greatest perpendicular distance between parallel faces is less than 0.375 inch.
WIRE EDM Is an electrical discharge machining except that a wire is used as the electrode and the dielectric is frequently ionized water. These machines are numerically controlled and computer programmed.
WROUGHT PRODUCT A product that has been subjected to mechanical working by extruding, rolling, forging or other processes.
Back to top


