although features ( i ) to ( iii ) detailed above are known in the electro - plating art , feature ( iv ) is considered to be novel both alone and in combination with features ( i ) to ( iii ). in carrying out the process of the present invention , the anode ( or plurality of anodes ) may be made from any electrically conducting material , and the cell is operated substantially in a direct current w mode , although polarity reversal may optionally be used during a minor part of the time of operation . to operate the process of the invention , a dc voltage is applied between the anode and the cathode ( workpiece ) and the electrolyte is introduced into the gap between the anode and the cathode by any suitable means such as flowing , spraying , atomising , jetting or dropping , whether through one or more holes in the anode or otherwise , but without producing immersion of the workpiece . it is necessary to strike ( that is , initiate ) the arc and this may be done in several ways . one effective way is to set the voltage and electrode separation and then introduce the electrolyte . initially at a rate ( the ‘ flow - rate ’) high enough to prevent arc formation between the anode and the cathode . the flow - rate is then progressively decreased until the plasma arc occurs , becoming visible to the naked eye , at which point rapid deposition of the metal or metal alloy coating occurs . the plasma arc does not necessarily fill the gap between the anode and the cathode ; there is normally a considerable dark space on the anode side . metal deposition rates can exceed a thickness of 60 micrometres per minute at current densities no greater than 100 amp / dm 2 compared with a normal value of about 10 micrometres / minute and up to 20 micrometres / minute for fast conventional electroplating processes carried out at comparable current density . the nature of the coating obtained using the method of the invention may be different from that obtained using conventional electro - plating process , as is described later . as the flow - rate is further reduced beyond the point at which an arc is struck , the intensity of the plasma arc increases until eventually it reaches a maximum and begins to fall again . once the flow - rate is reduced to zero , neither arc formation nor deposition occurs . for any fixed values of other material variables ( namely voltage , anode - to - cathode distance , and electrolyte temperature ) there is therefore a range of flow - rates over which the process can be operated . this range will depend upon the values chosen for the different variables , as well as on the electrolyte composition . it is to be understood that the method described for striking the arc is by way of example only and that other methods can be used , such as a gradual increase of the voltage whilst maintaining other variables constant . optionally , sacrificial anodes of the metal or metals to be deposited may be disposed within the cell and in contact with the electrolyte to help maintain the electrolyte concentration as is well known in the art . the workpiece may be of any shape or form as long as the anode can be kept at a substantially constant distance from the workpiece . for example , the workpiece comprises a metal strip , metal sheet , metal slab or a pipe . the surface of the workpiece which is electroplated in accordance with the invention is that of the cathode . the ranges of variables within which useful results can be obtained are as follows : the range of voltages employed in the method of the present invention is generally in the range of from 50 to 300v dc , which is relatively high and considerably higher than the range of 5 to 20v dc used in conventional electroplating processes . the current density may vary in the range of from 1 to 200 amp per square decimetre of anode ( amp / dm 2 ). the flow rates may vary quite widely , between 0 . 2 and 25 litres per minute per square decimetre of anode ( 1 / min . dm 2 ) the electrolyte comprises an aqueous solution of one or more compounds of the metal or metals to be coated . typical concentrations are from 1 % by weight to saturation . typical examples of solutions which may be used are as follows : temperatures in the range of from 10 to 90 ° c . can usefully be employed . it will be understood that appropriate means may be provided in order to heat or cool the electrolyte and thus maintain it at the desired operating temperature . the anode - to - cathode separation , or the working distance , is generally within the range of from 3 to 30mm , preferably within the range of from 5 to 20 mm . it will be understood that arcing cannot necessarily be obtained with any combination of variables within the ranges detailed above , but only under some combinations thereof . the combinations which will work may depend on the electrolyte composition , the metal to be coated , the shape , size and mass of the workpiece , and the configuration of the electrolytic cell . in order to establish whether a given combination of variables will initiate and support arcing , all that is required is to fix all the named variables except one and then vary that last variable over its range . as indicated earlier , the easiest parameter to vary is the electrolyte flow - rate . the coatings may be of any metal or combination of metals which have soluble salts or soluble ionisable compounds . typically the coating obtained will consist of two layers which merge with each other , namely a solid continuous layer adjacent to the original workpiece surface ( bottom layer ) and a porous layer adjacent the solid continuous layer ( top layer ). this solid / porous dual &# 39 ; structure provides both a solid barrier to corrosion and a porous top layer which provides an excellent surface for mechanical keying of subsequent coatings ( e . g . plastic or paint ) and provides protection against mechanical damage . the structure of the coating will depend upon the precise conditions employed and coatings of a different structure from that described above may also be obtained , for example , completely solid coatings . the maximum deposition rate is fast when compared to conventional electro - deposition methods at comparable current densities , and can exceed 1 micrometre per second ( 60 micrometres per minute ). coating thickness can be controlled by , among other things , traversing the workpiece through the cell [ working zone ] so that it moves relative to the fixed anode but at a constant separation from the anode . the time spent in the working zone will be inversely proportional to the speed of traverse and the coating thickness will be pro rata to the said time . the workpiece may be passed several times through the same working zone , or through several working zones sequentially . the high coating speeds available mean that the process is particularly useful for on - line or continuous - process treatment of metals . the present invention will be further described with reference to the following examples . a pre - cleaned mild steel plate 0 . 31 cm ( 0 . 125 ) inch thick forming the cathode in an electrochemical cell was coated with a mixture of zinc and aluminium under the following conditions . after a treatment time of 80 seconds , a layer of zinc / aluminium approximately 27 micrometres thick was deposited onto the cathode consisting of a bottom solid ( compact ) layer adjacent to the steel cathode substrate and a top porous layer . when tested for coating adhesion to the substrate using astm ‘ pull off ’ test no . d4541 - 95 , the average pull - off stress was 39 mpa which exceeds industry standards . when tested for cathodic disbandment by industry standard tests , the disbanded distance was under 2 mm after 24 hours and under 3 mm after 48 hours , which values are far superior to industry averages values of 8 mm and 12 mm , respectively . a thin pre - cleaned strip of mild steel 19 mm wide and 2 . 1 mm long forming the cathode of an electrochemical cell was coated with a mixture of zinc and aluminium as in example 1 under the following conditions : the steel strip was passed through the working zone of the cell 5 times , each pass taking 36 seconds . this corresponded to a 10 second total treatment time for any one area of the cathode . a layer of zinc / aluminium approximately 6 to 10 micrometres was deposited on the cathode . the general procedure of example 2 was repeated using a mild steel strip sample 6 . 2 cm wide and 21 cm long and a saturated zinc sulphate solution as electrolyte . the progressive deposition of zinc , in terms of the thickness of the coating layer , as a function of the time of treatment is shown in fig1 . the deposition rate exceeds 1 micrometre per second . the layer of zinc deposited in example 3 consists of a solid layer ( n ) approximately 5 micrometres thick adjacent to the steel substrate . this structure is illustrated in the scanned and digitized electron micrograph image of fig2 . an eds ( energy dispersive spectrometer ) analysis of various areas ( n , o , p & amp ; q ) in the cross - section showed : the procedure of example 2 was repeated under the following conditions : electron micrographs of a cross - section of the coated steel showed that a solid ( non - porous ) coating of zinc , some 10 micrometres thick , had been deposited on the steel .