US3167403A - Base materials coated with an alloy of aluminum and manganese - Google Patents

Description

Jan. 26, 1965 sM ETAL 3,167,403

BASE MATERIALS COATED WITH AN ALLOY OF ALUMINUM AND MANGANESE 3 Sheets-Sheet 1 Filed June 9, 1960 ELIE-E .1.

I H, l, I/ f,/ /;l/;/ H41 59 so as INVENTORS EDWIN J. SMITH MICHAEL G. VUCICH E11: ElEu BY LOWELL W. AUSTIN M qdfLQ/Q A TTORNEYS Jan. 26, 1965 Filed June 9, 1960 CURRENT DENSITY (Amperes per Sq. H.)

E. J SMITH ETAL 3,167,403

BASE MATERIALS COATED WITH AN ALLOY OF ALUMINUM AND MANGANESE 3 Sheets-Sheet 2 EFFECT OF MANGANESE CONCENTRATION AND CURRENT DENSITY ON BRIGHTNESS UNIFORMLY SEMI- BRIGHT BRIGHT DARK MATTE o I I 1 %MANGANESE IN BATH (wr. Mn m mm! wmr Bath) 3 INVENTORS 2' T EDWIN .1. SMITH MICHAEL G- VUCICH BY LOWELL W. AUSTIN A TTORNE Y8 WEIGHT PER CENT MANGANESE IN FREE ALUMINUM AND MANGANESE OF BATH WI. Mn x Jan. 26, 1965 Filed June 9, 1960 Wt. free Al W. Mn) N o E. J. SMITH ETAL 3,167,403

BASE MATERIALS COATED WITH AN ALLOY OF ALUMINUM AND MANGANESE 3 Sheets-Sheet 3 o 80% A! 0/ 70% A! 01 Na 0/ Na 0/ K 10% KC! 15% KC! AI a 7.5% Na c: 7.5? KC! D F G o AICI3 H 5% NaCl o 6.2 o.'4 0:6 0.5 [o

WEIGHT PER CENT MANGANESE IN BATH w'. Mn x I00 Total WI. of Bath IN VEN TORS EDWIN J. SMITH MICHAEL G. VUCICH LOWELL W. AUSTIN A TTORNE YS and in the absence of special plating conditions.

United States Patent Orifice 3,l67,43 ?atentecl Jan. 26, 1965 3,167,403 BASE MATERIALS CGATED WITH AN ALLQY F ALUMINUM AND MANGANElE Edwin J. Smith, Steubenville, Ghio, and Michael G.

Vucich and Lowell W. Austin, Weirton, W. Va, assignors to National Steel orporation, a corporation of Delaware Filed June 9, 1960, Ser. No. 34,9 23 8. (Ilaims. (Cl. 29-4962) This invention broadly relates to the coating of base materials with an alloy of aluminum and manganese and the resultant coated products. In some of its more specific aspects, the invention relates to the electrodeposition of alloys and, more particularly, to the electrodeposition of an alloy of aluminum and manganese. The invention further relates to a novel method of producing bright aluminum electroplate in the as plated condition, a novel electrolyte bath, and the products produced in accordance with the invention.

This application is a continuation-in-part of our copending application Serial No. 819,298, filed June 10, 1959, now abandoned.

One embodiment of the present invention will be de scribed and illustrated hereinafter with specific reference to electroplating an aluminum-manganese alloy on ferrous metal strip using a fused electrolyte containing a major proportion of aluminum chloride and the remainder one or more alkali metal chlorides such as sodium or potassium chloride. However, it will be apparent to those skilled in the art that the principles of the invention are applicable to other metal bases, forms of metal bases, and fused salt electrolytes in general for electroplating alumi num. Also, that other methods may be employed for coating metallic or other suitable base materials with an 7 position being exemplified by a composition containing by weight 80% aluminum chloride and 20% sodium chloride and a satisfactory ternary electrolyte being exemplified by a composition containing by weight 80% aluminum chloride, 10% sodium chloride and 10% potassium chloride. Although a fused electrolyte bath containing 8085% aluminum chloride produces objectionable visible fuming in the presence of water, an electrolyte containing more than 85% aluminum chloride fumes excessively and the plating results usually are not improved by increasing the aluminum chloride content above this value. If the aluminum chloride content falls below about 75% by weight, poor plating results when using unmodified direct current Thus, such electrolyte compositions usually are not preferred. However, it is possible to use electrolyte compositions containing less than 75 aluminum chloride and the remainder alkali metal chloride when using special plating conditions and/or by using low current densities. For example, non-fuming baths maintained in the molten state at a temperature of about 190200 C. and containing less than 70% aluminum chloride, e.g., substantially no free aluminum chloride, may be used to electroplate satisfactory adherent, non-powdery aluminum deposits when using straight direct current at current densities less than one ampere per square foot, at current densities less than one ampere per square foot when using polarity reverse current, at current densities up to two amperes per square foot when using pulse direct current, and up to fifteen amperes per square foot when using a hot cathode maintained at a temperature much higher than the bath temperature. At higher bath temperatures within the operative range, current densities may be raised to some extent without resulting in the deposition of powdery deposits or deposits having other imperfections. With slightly fuming aluminum chloride-alkali metal chloride baths, i.e., electrolyte baths containing about 70% aluminum chloride and the remainder alkali metal chloride and having a free aluminum chloride content of about 0.5- 1.5%, the current density may be up to five amperes per square foot when straight direct current is used, up to ten amperes per square foot when polarity reverse current is used, above fifteen amperes per square foot when using a hot cathode maintained at temperatures much higher than the bath, and considerably above 18.6 amperes per square foot when using pulse direct current. When using a fuming aluminum chloride-alkali metal chloride bath, such as a bath containing aluminum chloride, 10% sodium chloride and 10% potassium chloride, current densities up to amperes per square foot and often as high as 100-400 amperes per square foot may be used with straight direct current, with the current densities for special plating conditions being equally satisfactory or even better. Thus, it is apparent that a wide variety of aluminum chloride-alkali metal chloride electrolyte baths are suitable for the electrodeposition of aluminum on a metal base such as ferrous metal and that any suitable one of these baths may be used in practicing the present invention. In general, the electrolyte baths for use in practicing the present invention are prior art aluminum electroplating baths containing the novel additive to be discussed hereinafter.

Still other aluminum electroplating baths are known to the art and may be used in practicing the present invention. For example, one or more of the chloride salts of the baths mentioned herein may be replaced with other suitable halide salts such as aluminum bromide, sodium bromide and potassium bromide in the molar proportions existing in the above mentioned baths. nurn chloride may be complexed with other complexing agents such as ammonia, organic amines, or their salts in a manner somewhat similar in effect to the complexing of aluminum chloride in the foregoing baths with potassium and/or sodium chloride. An aluminum chlorideamrnonia bath contains complexed aluminum chloride which is thought to be in the form of AlCl .NH or possibly higher members of the ammonia series with varying amounts of free aluminum chloride being dissolved therein in the case of the fuming bath, or a non-fuming bath may be used as discussed above for the more common aluminum chloride-alkali metal chloride baths. Further, aluminum chloride may be complexed by means of organic amines and their salts such as ethyl pyridinium bromide to produce the complex ethyl pyridinium bromide-AlCl This material may likewise have free aluminum chloride dissolved therein or it may be a non-fuming bath as discussed above.

The various fused salt aluminum electroplating baths discussed above may be considered to be, broadly speaking, electrolyte baths containing aluminum halide and a complexing agent therefor with the aluminum halide complex being in the molten state and having dissolved therein free aluminum halide in instances where it is present. Such fused salt electrolyte bath compositions known to the art to be suitable for the electroplating of aluminum and capable of dissolving the additive to be discussed hereinafter are operative in practicing the present invention.

It is understood that when substituting other halides for chlorides in the electroplating baths discussed herein, the substitutions will be made in molar proportions rather Also, the alumimolar proportion of aluminum halide, the complexing agent therefor and the free aluminum halide dissolved Organic-type baths for electr plating aluminum also i are known. Such baths may. contain an organic compound such as an organic solvent or organo-metalhc compounds. The. composition, preparation and use of organic-type baths for the electrodeposition of aluminum are described in numerous publications and patentsincluding United States Patents 1,911,122, 1,939,397,

as protective coatings for corrodable base materials, and

thus the products voffthe invention are characterized by excellent corrosion resistance.

In accordance with one important embodiment ofthe present invention, it has been discovered that aluminum may be. electroplated in the form of a coating which is bright, lustrous and reflective by adding manganese to a prior artgele'ctroly-te bath for electroplating aluminum. The resultingflelectroplateis bright, lustrous and reflective and resembles tinplate somewhat in this respect. .Further brightening is not necessary and it is ready as plated for use in the manner of tinplate.

It is an object of the present invention to provide novel methods of coating. base materials'with an alloy of aluminum and manganese. 1

It is a further object of the present invention to prepare novelcoated products wherein a base material is provided When electroplating bright aluminum deposits in the form of an aluminum-manganese alloy in accordance with the teachings of the present invention, the above electroplating baths may be used under the same conditions as when electrodepositing aluminum matte. In fact, no suberally speaking, other than in providing the proper additive concentration inthe electrolyte bath. An example of a highly satisfactory method and apparatus for electroplating aluminum from aluminum halide-alkali metal chloride baths is disclosed inf'copending application Serial "No. 665,743, filed June. 14, 1957, by Edwin J. Smith and Michael G. Vucich for Plating Apparatus, and Method, the

:stantial change in operating conditions .is necessary, 'genan additive.

with a coating ofian alloy of aluminum and manganese. It is a further objectofthe present invention to provide a novel method of the electrodeposition of aluminummanganese alloys. T

It is a further object of the present invention to provide a novel method of producing aluminum electroplate which is brightin the as platedcondition.

It is s'tillafu-rthe'r' object of the present invention to provide "a novel method of electroplating bright aluminummanganese alloy coatings on a metal base using an electrolyte for electroplating aluminum containing manganese as It is still .a further object ofthe present invention to provide an: electroplated alloy of aluminumand manga'nese containing at:least about 10% manganese and the baths under A commercial applications and matte aluminum electroplate 'of the prior art is unsatisfactory, many attempts have been made to convert the usual white matte electroplated surface to a bright, reflective surface resembling tinplate. .The only practical method availableheretofore for brighttained by this method depends upon several factors such This method invariably results in of aluminum on the rollsu or. to regrind the rolls. It

'is impractical. to refiow aluminum mattein' the manner of tinplate where thin coatings are applied due to rapid alloying of aluminum with steel at the elevated temperatures required to melt the aluminum.- Also, attempts to.

reflow aluminum electroplate where thin coatings-are ap-. plied have resulted in coatingswith a dark, dull'appearance. This is believed to be due to the fact that aluminum and ferrous metal alloy too rapidly to leave a bright reflowed layer of aluminum. In view of the foregoing, it may be seen that the two'usual methods of brightening ening white matte deposits of aluminum has been by pass- 5 ing the matte through smooth highly polished [rolls to which pressure is applied. The degree of brightness ob-f w chloridetand partially in cross section,- of

. the purpose of. clarity;

remainder' 'aluminum together .with incidental impurities. It is still a further object ofthepresent invention toprovide novel electrolyte baths, suitable for use in, practicing the presentv invention. 1

. Still other. objectsofthe present invention and the advantages thereof will be apparent to those skilled in the artupon reference to the following detailed description and the drawings, wherein: FIGUREl is a diagrammatic side elevational view, apparatus for use in practicing the present invention; 7

FIGURE -2'is a cross-sectional view taken along the line 2-.2 of FIGURE 1 but omitting a showing of the strip, the sealing flaps, the rolls, and the electrodes for FIGURE- 3' graphically illustrates the effect of manfganeseconcentrati'on and current density on brightness of the aluminum-manganese alloy. coating. when using .an electrolyte bath containing by Weight 80 parts aluminum 'chloride, 10 parts sodium chloridean-d 10 parts potassium FIGURE 4 graphicallyillustrates the relationship between 7 the 'weight percent of manganese in the bath and the, weight percent of manganese based on the total weight 'of free aluminum and manganese in the bath when producing bright aluminum-manganese electroplate.

Referring now to FIGURES 1 and 2 ofthe drawings,

which illustrate a specific embodiment of the invention,-

the ferrous metal strip 10'after receiving a wet prior art treatment or other suitable pretreatment such as cathodic matte electroplate have proved to be entirely unacceptable;

"num and manganese may be deposited on base materials to provide novelcoated products by a number of methods. It has been further discovered that such alloy coatings have properties which render them remarkably effective cleaningin' an Orthosil solution Na SiO employing a treatingltime of 1-2 seconds at a current density of 35 ampere seconds per square foot, followed by, in sequence, brushingand spraying'withiwater, ,anodic pickling in a :suitable electrolyte such asaqueous 35% sulfuric acid for 2-3 seconds at -100 amperes persqua-re foot, scrubbing and washing with water and drying to remove all traces of'water, isshown passing lJIldBI'Jl'Oll. 11. The strip 10 then passes upwardly through heater 12 where it is heated ,sufiiciently to completely evaporate any free water reoperating conditions.

l3 traces of free water and then passes over rolls 16 and 17. If desired, the ferrous metal strip may be treated within strip conditioning unit in a reducing atmosphere or otherwise treated for the purpose of further conditioning the strip surface and assuring absolute removal of free water, combined water and substances forming water under the conditions present in the electroplating unit.

It also may be desirable to preheat the strip to a temperature about the temperature of the bath at the time plating is commenced. Two parts of suitable sealing flaps and 21 are provided near the entrance and exit ends, respectively, of strip conditioning unit 15 to prevent undue loss of any dry gaseous treating agent which may be employed in strip conditioning unit 15, as well as in aiding in preventing entry of atmospheric water vapor. The dry gaseous treating agent may be supplied to strip conditioning unit 15 by means of conduit 22 and withdrawn by means of conduit 23. The flow rate of dry gaseous treating agent to strip, conditioning unit 15 via conduit 22 is controlled by means of valve 24, while the withdrawal rate via conduit 23 is controlled by means of valve 25. Any suitable dry gaseous treating agent may be employed in strip conditioning unit 15 depending upon the nature of the treatment desired. However, it is essential that the treatment be such so as to insure that the surface of ferrous metal strip 10 is free of free water, combined water such as hydrated ferrous metal salts, or substances reacting under conditions present in the electroplating zone to form water upon exit form strip conditioning unit 15. In addition, it is essential once the strip has been thoroughly dried and freed of all sources of water that the dry strip not be subjected to any source of water while passing from the drying step to the electrolyte. It is preferred to surround the strip at all times with a dry medium, such as a dry, non-reactive gas, during pas a sage from the drying step to the electroplating bath. In instances where special conditioning treatment is not necessary, the gaseous treating agent may be dry air, nitrogen,

carbon dioxide, argon, etc. Usually, it is preferred that the gaseous treating agent be supplied through strip conditioning unit 15 at about atmospheric pressure.

The ferrous metal strip 1% passes downwardly from strip conditioning unit 15 into electroplating tank 28 containing an aluminum electroplating electrolyte such as herein described. The electrolyte 29 may be a fused electrolyte containing a predominant proportion of aluminum chloride such as for example 80% aluminum chloride, 10% sodium chloride and 10% potassium chloride on a weight basis and when such an electrolyte is used it fumes in the presence of water or water vapor under the A hood 30 is positioned above electroplating tank 28, as best seen in FIGURE 2. The exit end 31 of strip conditioning unit 15 extends downward a short distance through opening 32 in hood 3t and, similarly, the entrance end 33 of unit 36 extends downward a short distance through opening 37 in hood 30, thereby providing an entrance and an exit, respectively, to electroplating tank 28 for ferrous metal strip 10. The hood 3% is joined to both strip conditioning unit 15 and unit 36 in air-tight relationship, and since sealing flaps 2-1 and 38- are provided near ends 31 and 33, respectively, this combination of elements substantially seal off electrolyte 29 from the surrounding atmosphere. A gas or gaseous mixture such as dry nitrogen, carbon dioxide, argon or air is fed by means of conduit 39 into space All within electroplating tank 28 and above level 41 of electrolyte 29 and the undersurface of hood 30. A valve 42 is provided in conduit 39 for the purpose of controlling the feed rate of dry gas that is fed to space 40.

Electroplating tank 28 is provided with spaced pairs of aluminum-manganese alloy anodes 45 and 46-52. The foregoing anodes may be of high purity aluminum when an auxiliary source of maganese is provided, such as when manganese is added to the bath in the form of a manganese halide such as manganese chloride or other suitable manganese mineral acid salts soluble in the electrolyte bath 29, or manganese may be added to the bath by dissolution of auxiliary anodes containing manganese in an auxiliary electrical circuit. anodes and addition of a desired metal to an electroplating bath by means of their dissolution in an auxiliary circuit is Well known to the art and, although not illustrated in the drawings in the interest of clarity, it is understood that such a method of adding manganese is within the scope of the present invention.

The ferrous metal strip 10 passes downwardly from roll 17 into fused electrolyte 29 and is subsequently passed between the spaced pairs of anodes by means of a path established by rolls 55 and 56-61. The spaced pairs of anodes are electrically connected to the positive side of generator 64 (or other suitable source of current), while ferrous metal strip 143 is made electro-negative between contact rolls 1'7, 55, 57, 59 and 61 and the corresponding pairs of electrodes operably arranged with respect to each of the rolls by means comprising an electrical connection between the rolls and the negative side of generator 64. The ferrous metal strip 10 is electroplatedwith a coating of aluminum-manganese alloy containing at least about 10% manganese and the remainder aluminum. The coating may be of any suitable desired thickness and will be bright in the as plated condition regardless of the thickness since the thickness of the electroplate appears to have little or no effect on its brightness. However, as is true of other electroplating processes producing bright electroplate in the as plated condition, it is advantageous to provide a smooth surface on the strip 10 and it should not be subjected to a strong pickling action. The brightest plate is produced on smooth steel given a short pickle at low current densities. Overetching of the surface results in a somewhat duller finish although the electroplate still is bright as plated.

When the electrolyte contains by weight aluminum chloride, 10% sodium chloride and 10% potassium chloride the bath 29 may be at a temperature of about 250- 400" F. and, preferably, about 300-350" F. Current density, preferably, should be from 20 to about amperes per square foot. However, under optimum conditions of operation, current densities up to about 100 to 400 amperes per square foot are possible and may be used when desired. As previously mentioned, the electroplating conditions for use in accordance with the present invention need not differ in any respect from those of the prior art for electroplating substantially pure matte aluminum deposits other than in providing the proper manganese con centration in the electrolyte bath. It is understood that plating conditions will necessarily vary somewhat from electrolyte to electrolyte. However, suitable, conditions for a given prior art electrolyte for the electroplating of aluminum are well known to those skilled in the art and may be selected as if aluminum alone were to be electro plated.

After passing under roll 61, the ferrous metal strip 10 passes upwardly through electrolyte 29 and after emerging therefrom passes between squeegee rolls 65, which reduce the amount of dragout of electrolyte to some extent. The ferrous metal strip 10 continues to pass upwardly through unit 36 and is then passed horizontally over roll 66. A pair of sealing flaps 67 are provided at the exit end .35 of unit 36 for the purpose of sealing off the exit and thereby allowing a slight suction to be applied to unit 36 through exhaust conduit 653 when this may be desired, as

well as preventing entry of atmospheric water vapor which 7 would have a detrimental effect on the aluminum chloride content of the electrolyte. The exhaust conduit 68 is providedwith valve 69 for the purpose of controlling exhaust of unit 36 in instances where it is exhausted. The plated ferrous metal strip 10, after passing over roll 66, passes from the exit end of unit 36 and then may be Washed with water and dried or given other subsequent treatments. However, the washed and dried electroplate is generally The provision of auxiliary ganese does not. r p V Manganese should be added to the electrolyte bath in amass very satisfactory forlusedirectly in the manufacture of containers of the typefor which tinplate is generally used. Since the aluminum-manganese alloy electroplate does not require flow brightening, roll brightening or other brighten- 'ing steps, the customary brightening step following electrodeposition'of pure aluminum coatings is completely eliminated. The electroplated strip emerging from unit 36 is bright, lustrous and reflective in the as plated condition.

For the purpose ofminimizing loss of heat, electroplating tank 28 maybe surrounded by aninsulating material,

70. Additionally, and in order to maintain the fused electrolyte 29 at the proper operating temperature, heating means (not, shown) may be employed asis conventionalin the art. For example, immersion heating may-be employed in the conventional manner wherein the heating units are immersed directly in the electrolyte or, preferably, the insulating material.70 maybe spaced from the electroplating tankZS and the electroplating tank surrounded within the space thus formed by'suitable heating means such as fin-type strip electricaljheaters g anese, may be directly added in the form of anhydrous ,manga'nesesalts such as anhydrous manganese chloride,

I andj' this method of addition is especially'ed'esirable when commencing operations and'preparingthe fused body of electrolyte preliminary to plating. Also, auxiliary anodes of manganese may =be used; -andfmay be electrically The gas or gaseous mixture fed through conduit 39 must 7 'be dry, but it may be at any suitable convenient temperature such as room temperature. The pressureernployed "-be maintained, if desired, 'on strip conditioning unit '15 and unit 36 by means of exhaust conduits 23 and 68, re-

spectively, to aid in the escape ofgas fed to space together with any moisture or water content through flexible sealing flaps 21 and 38. It is not necessary that the gas 40 maintained under a, substantially elevated pressure.

However, a pressure above atmospheric pressure may be The com position of the specific dry gas-or 'dry gaseous mixture 7 supplied tospac'e 40 may vary Widely. It is only neces- 'sary that the dry gas or gaseous mixture be substantially non-reactive under the conditions of operation of the electroplating line with the electrolyte 2 9, the strip '10 'or-the.

preferred in some instances for best results.

apparatus contacted by the gas or gaseous mixture.

It is surprising that aluminum and manganese readily 'within space 40 may be atmospheric pressurejor slightly above although any suitable;convenient-pressure;may be applied. It is only necessary to replace the atmosphere within space 40 with a dry gas and, a slight suction may connected in theusual manner for dissolution of an auxiliary anode, as iswell known in the art. fWhen organictype baths are used, then a suitable manganese compound such as an organo-manganese compound may be added to provide thedesired manganese content. Regardless of the method of addition of manganeseand whether or not the manganese bearing material added to the bath is a salt of manganese; suchas manganese chloride or other mangane-se salts of a-min-er-al acid, pure manganese or nnanganese alloy anodes, or other suitable source of manbe supplied under pressure or the atmosphere within space V ganese containing materials and substances, the markedly improved appearance of the'aluminum coating will be :efiected provided the proper manganese concentration of :the electrolyte bath is reached.

The amount of manganese to be added to the bath will vary somewhat fromelectnolyte to electrolyte; Broadly speaking, however, manganese in itheiform of, a simple codeposit in the form of an aluminum-manganese alloy which is bright in the as plated condition.- This is espe cially true since it has been found that other heavy metals affect the color of the coating. For example, amounts of duce black or unsatisfactory discolored coatings, while small amounts of lead will produce milky to gray coatings. Also, these metals all will tend to'precipitate from the electrolyte upon standing in the presence of aluminum or aluminum anodes while it has been discovered that mansuch as iron, copper, lead, nickel, etci, tend "to adversely iron in the bath in percentages as low as 0.02% will pro- 1 an amount to provide the desired percentage of manganese in the resultantaluminum-manganese alloy coating. Generally speaking, when the alloy coating contains at least 10% manganese and, preferably, 10-70% manganese and the remainder aluminum with incidental impurities, then the electropla'te is bright as plated However, amounts such as 16-30% manganese and 84-70% aluminum to- 'gether with incidental impurities generally give more form and brighter deposits. About 16-20% manganese and a'bout'84-80% aiuminuniarepreferred in most instances as manganese contents greater than about 20% do not seem to further improve corrosion. cesistance. When the all-oy contains 10-16% manganese, then it should be deposited at high current densities and with agitation in order to assure the hestresults, Under the proper rentdensity on bri'ghtness for stillplating when using a manganese salt may be present inthe electrolyte in an amount providing about 10-70% by weight, and preferably, 16-30% by weight of manganese when based upon the total Weight of manganese in the dissolved-free man- .ganese salt and aluminum in the free aluminum chloride. Thus, when a major proportion of the aluminum chloride is comp-lexed as NaAlClyor KAlCh, as-in the case-0f a bath containing 80% by weight aluminum chloride, 10% sodium chloride and 10% potassium chloride,

'srn-all additions of manganese areetfectivea For example, .a manganese concentration as little ,as 0.2% by weight .Wlll produce brightplate provided the current density is highandlthere is proper agitatiomwith uniformly bright .plat-ejbeing obtained atall current densities when the bath contains at least 05 manganese. Larger additions'of manganese may be made to o'btainqadesired'liigher man- ;ganese content in 'the electroplated alloy, but percentaia'gesggreater than about 1%, are usuallyhot necessary or desired al-thoughiamouuts'up 102, 3, 4 or 5% or :higher; percentages may be used in some instances. Pref- V er-ably, the above bath should contain about 0.5-1% manganese'. Organic-type baths may contain concentrations of manganese providing -about,- 10-70%@ and, preferably,

1 16-30% ot-manganese in the resultant coating.

Upon reference to FIGURE 3 of the drawings, which illustrates the effect of manganese concentration and curbath containing 80 parts aluminum chloride, 10 parts sodiu-m chloride and 10 partspotassi-um chloride, by weight,

conditions, very good results are obtained when e'lectroplating a coating containing about 10, 11 or 12% manganese and the remainder aluminum together with incifldent al impurities. Amounts of manganese larger than 6 it may be noted that, if the bath contains atleast 0.5% fplatejis .b'right at practical current densities as illustrated by the area to the right of curve C. At manganese concen- W trationsof about 02-05%, whether or nota brig-ht coatmanganese, then the resultant aluminum-manganese alloy ing as plated is obtained depends upon the current density,

with bright coatings being obtained at about 100 amperes per square, foot. whenithe manganese concentration is 10.25 at about 60 amperesper square foot when the man ganese concentration is. 0.3%, and at about '25 amperes per. square foot when the manganese concentration is 0.4%. At manganese concentrations less than 0.25%, semi-bright or dark matte coatings are obtained in the area to the left of curve C. The above mentioned bath contains 66.8% by weight of aluminum chloride complexed as NaAlOL; and KAlCh, thus leaving 13.2% by weight free aluminum chloride or 2.67% by weight free a l-urninum in the bath.

FIGURE 4 of the drawings graphically illustrates the relationship between the weight percent of manganese in the bath and the weight percent of manganese based on the total weight of free aluminum and manganese in the bath when producing bright aluminum-manganese alloy electroplate from electrolyte baths'of varying compositions. The curves D, E, F, G and H are based on calculations for electrolyte bath compositions containing 70, 75, 80, 85 and 90 Weight percent aluminum chloride, respectively, with the remainder or the compositions being equal parts by weight of sodium chloride and potassium chloride. When the weight percent of manganese based on the total weight of manganese and free aluminum, i.e., aluminum contained in the aluminum chloride content of the bath which is not complexed as NaAlCl, or KAlCl rises to about 16% or higher, then uniformly bright electroplate is always produced. Thus, the area above line K represents an area in which uniformiy bright electroplate is produced under all plating conditions. At weight percent manganese concentrations of at least and up to 16%, i.e., in the area between lines I and K, uniformly bright electroplate is usually obtained only under preferred plating conditions. For example, the current density should be 20-100 amps./ sq. ft. or higher and preferably with agitation. in the area below line I, i.e., at manganese concentrations below about 10%, uniformly bright plate is not usually obtainable although bright areas may be present.

It has been found that higher current densities within the operative current density range for a given electrolyte bath will produce smoother and brighter plate at low concentrations of manganese. Improved deposits, in some instances, also may be obtained by using special current or plating conditions such as pulsating current,

polarity reverse current, a hot cathode maintained at a temperature substantially above that of the operating temperature of the bath, agitation, etc. Also, higher operative current densities for the same bath may be possible when using such aids and, as pointed out above, this is advantageous since higher current densities produce brighter deposits at low concentrations of mangadeposition, cathode sputtening, metal spraying, and decomposition or reduction of volatile compounds of aluminum and manganese. When using a method other than electroplating for forming the alloy coating, then it may contain about 1-70% manganese and, preferably,

1-30% manganese by weight and the remainder aluminum together with any incidental impurities. However, manganese contents above about 20% by weight do not usually result in further improvement in corrosion resistance.

When a hot dipping method is employed, a metal base such as ferrous metal strip is immersed in a molten bath of an alloy of aluminum and manganese and then withdrawn. The resultant coating of molten alloy on the metal base is then solidified. The composition of the molten bath is adjusted to provide an alloy coating on the metal base containing about 1-70% manganese, and preferably about 1-30% manganese and about 99-70% aluminum together with any incidental impurities. Hot dipping methods of applying aluminum to base metals are well known to the art, and such methods may be modified by providing a molten metal bath as discussed above rather than relatively pure molten aluminum. Examples of patents relating to the application of aluminum by hot dipping methods include US. Patents 2,751,311 and 2,918,388. The melting points of aluminummanganese alloys are about 660 C. and higher for alloys containing 1% or more manganese by weight. For aluminum-manganese alloys containing 10%, 20%, and 30% by weight manganese, the melting points are about 790 (3., 870 (3., and 950 C., respectively. Usually, the temperature of the molten bath should be suiiiciently above the melting point of the specific alloy used to provide a working range such as 50100 C. For example, when an aluminum-manganese alloy containing 10% manganese is applied, the bath temperature may be about 850 C.

The aluminum-manganese alloy coatings of the present invention also may be deposited on various substrates such as metals, including ferrous metal, and organic substrates such as plastics and paper by vacuum deposition echniques. C ne method involves deposition of an interspray of aluminum and manganese vapor. The aluminum and manganese vapor may be formed by using separate vapor sources such as heated crucibles or filmtype evaporators may be used. Alternatively, an alloy of appropriate composition may be heated in a single crucible and evaporated, or a film-type evaporator may be used. Regardless of the method of forming the interspray of aluminum and manganese vapor, the resultant mixture of vapor is deposited on the metal to produce an alloy coating containing 170% manganese and preferably 1-30% manganese and 99-70% aluminum together with incidental impurities. Alternatively, separate aluminum and manganese vapor sources may be used and thin alternate layers of aluminum and manganese deposited followed by'appropriate diffusion treatment at elevated temperature for a period sufficient to eifect appreciable diffusion with al-loy formation. In practicing this method, either the aluminum or manganese may be deposited in the form of a thin layer first, followed by deposition of a thin layer of the other metal. A plurality of aluminum and manganese coatings may be deposited alternately, if desired. The vacuum deposition of metals is well known in the art and is disclosed in numerous patents such as US. Patents 2,903,547 to Paul Alexander and 2,930,879 issued to Scatchard.

Cathode sputtering may be used to deposit the aluminum-manganese alloy coatings of the invention following the general procedure disclosed in prior art publications and patents such as U.S. Patents 2,200,909 and 2,257,411. Such processes are modified to provide a cathode which is an alloy of aluminum and manganese wherein the aluminum and manganese disintegrated from the cathode and deposited on the substrate is in the form of a coating containing 170% manganese and preferably 130% manganese and 99-70% aluminum together with incidental impurities. In practicing the method, a base material is coated with an alloy of aluminum and manganese by providing an anode and an aluminum-manganese alloy cathode in spaced relationship and impressing a voltage across the cathode and anode to disintegrate particles of aluminum and manganese from the cathode. The base material is contacted with the panticles of aluminum and manganese to deposit a coating of the alloy of aluminum and manganese thereon.

Still another method of applying the aluminum-manganese alloy coatings of the present invention is by spraying. The metal base to be coated is sprayed with a molgether with incidental impurities. 'tions and patents disclose suitable decomposable or relmixture of metals.

class of materials of great technological importance.

ten alloy of aluminum and manganese to form a molten alloy coating thereon and then the coating is solidified. 'The sprayedmolten alloy has a composition providing an alloy coating containing 1'70% manganese and preferably 130% manganese and 99-70% aluminum together with any incidental impurities. I The base material to be coated may be metals such as ferrous metal and the molten metal may be sprayed in accordance with US. Patents 2,490,543 and 2,845,366.

The aluminum-manganese alloy coatings of the present invention also may be deposited by decomposition or reduction of volatile compounds of the respective metals. For instance, a mixture of heat-decomposable compounds of aluminum and manganese may be formed and the mixture subjected to a temperature at which the compounds decompose to form metallic aluminum andmanganese which is deposited on the base material toform an alloy 'coating thereon. Alternatively, a mixture of compounds of aluminum and manganese which are reducible to metallic aluminum and manganese may be formed, and the ganese which is deposited on the base material. There- 'sultant alloy coatings may contain 170% manganese and preferably 1-30% manganese and 99-70% aluminum to- Nur'nerous' publicamixturereduced to produce metallic aluminum and manducible manganese and aluminum compounds, including. 7

'U.S. Patents'2,772,985, 2,880,115, 2,886,469, 2,898,235,

and 2,921,868 and the general procedures disclosed in these patents may be followed, modified as mentioned above in order to produce an aluminum-manganese coating of the desired. composition,

Surprisingly, the alloy coatings of the present invention exhibit vastly improved corrosionresistance over pure aluminum coatings. Also, the alloy may be" present in extremely thin coatings and yet excellent corrosion resist- For example, bright deposits of the coatings as determined by the ferri-cyanide porosity test is extremely low in even very thin coatings. 'In a conventional salt spray test, the improved, corrosion -resistance of aluminum-manganese alloy coatings is illustrated by the fact that 15-millionths of an inch'of alummum-manganese alloy- (80% Al20% Mn) is equivalent in resistance to red rust formation of 0.1 ounce/square foot of zinc, 7-millionths of. an inch of the above alloy is.

equivalent to 0.25 pound per base box of tin in resistance to red rust formation and corrosion tests'on-equal thicknesses ofthe alloy coating and pure'aluminum. coating show that the alloy coating is markedly superior to aluminum. There also is ,a diiferenceinthe nature, of the type of protection obtained when electroplating an aluminum-manganese alloy rather than aluminum alone. For example, the matte aluminum coatings of the prior art have been found to act as sacrificial coatings in the man- .ner of zinc, while aluminum-manganese alloy coatings have been found to act as barrier coatings in the manner of tin. This 'is a further unusual and. unexpected result lof the present invention which is'believed to be atleast partially responsible for the resistance. 1 V V The term alloy. is broadly used. herein when referring markedly improved corrosion .to the aluminum-manganese coatings of the invention. The term alloy is defined in The International Diction-' ary of Physics and Electronics, published by D. Van Nostrand Company, Inc., New York, New as follows:

York, 1956,

Generally speaking,

This defiriition covers an immense other, but form a superlattice.

- is maintainedin this condition 12 1 There are various types of alloys. Thus, the atoms of one metal maybe able to replace'the atoms of the other on its lattice sites, forming a subsiitutional alloy, or solid solution. the'sizes of the atoms, and their preferred structures, are similar, such a system may form a con- :tinuous series of solutionsotherwise the miscibility may be limited. Solid solutions, at certain definite atomic proportions, are capable of'undergoing an order-disorder transition into a state where the atoms of one metal are not distributed at random through the lattice sites of the Again, in certain alloy systems, intermetallic,compounds may occur, with certain highly complicated lattice structures, forming distinct crystal phases. It is also possible for light, small atoms to fit into the interstitial positionsin a lattice of a heavy metal, forming an-interstitial compound. v

The foregoing detailed description and the following specific examples are for purposes of illustration only and are not to be taken as limiting, to the spirit or scope of the appended claims. 7

(EXAMPLE I Ferrous metal strip wet-pretreated following the procedureset out incolumn 4, lines 59-75, of the specification and having a temperature/of about 325 F. is passed ,at a speed of ten feet per minute through plating apparatus similar to that illustrated in FIGURES 1 and 2 of the drawings, A feed of 72 cu. ft./hr. of dry gaseous nitrogen ispassed into the space between the hood and the electrolyte level and also intothe' strip conditioning unit for the purpose of preventing water contamination of the electrolyte due to the entrance of atmospheric moisture. The ferrous metal rstrip is dry after the pretreatment and completely free of"-free water, combined water'such as hydrated metal-salts and substances reacting under conditionspresent in the electroplating, zone to formwater and at the time of entering the electroplating zone. I g I. I

The stripis introduced into a fused fuming electrolyte containing by weight eighty parts aluminum, chloride, ten

parts sodium chloride and'ten 'parts potassium chloride 7 which'is maintained at a temperature of 325 F. Alumium-manganese alloy anodes (80% by Weight aluminum and 20% by weight manganese) ten feet in length are used employing a current density of 42.5 amps/sq. ft. to electroplate a coating thirty millionths of an inch thick of l j :bright aluminurmmanganese alloy thereon. 1 After plating,

a macroscopically homogeneous platewand .then subjected to scale pretreatment:

, the strip is fed from the electrolyte through the outlet zone and is washed in Water and dried." The aluminum-manganese alloy plate hasa bright, lustrous and reflective surface which is highly pleasing to the eye and which does v.not require. a brightening treatment of any'nature. Upon "analysis, the alloy coating contains about aluminum and 20% manganese. The'coating is adherent, dense, and

exhibits a lower porosity and higher corrosion resistance than aluminum elect'roplate having'a coating of equal thickness. Also, the coating is surprisingly ductile as evi- "denced by EricksonCup Tests. The electroplate may be formed into containers and the like in a manner analogous to thatof tinplate.

Following the above procedure, current densities up to amps/sq; ft. are satisfactory and produce good electroplate; 'Also, electroplate having ,an aluminum-manigane'se alloy coating thereon of from fifteen-millionths to "five hundred-millionths of an inch in thickness may be produced :Without impairment to the appearance of the coating; Y

l EXAMBLE Ii.

Panels were prepared from can making quality blackthe following wet laboratory (1) 15 second cathodic treatment at 10 0 amps/sq. ft. in

a hot 2 oz./gal; Orthosil solution; (2) Cold Water (70 F.) spray rinse;

13 (3) Anodic pickle in cold 17 Wt. percent sulfuric acid at 100 amps/ sq. ft. for 2 seconds; (4) Cold water (70 F.) spray rinse; (5) Hot water rinse-(180 F.);

tion were varied over wider ranges in electroplating panels with the aluminum-manganese alloy. The plating condi tions used, data obtained, and observations appear below in Table I.

Table I Panel 0.1). Percent Percent No. Amps. Sec. Coulombs Brightness (a.s.t.) Mn in Mn in Bath Coating S00 Matte-White 79 0 0 80 40 0 0 100 79 0 0 200 79 0 0 60 56 0 0 120 66 0 0 120 18 0.11 0.41

60 56 0.11 0 85 0.11 60 0.11 140 ,do 19 0.11 120 Edges Bright Only 19 0.21 50 do 59 0.21 35 875 do 98 0.21 150 750 Fairly Bright All Over But Some 19 0.32

Dull Streaks. 50 d 59 0.32 35 94 0. 32 45 78 0.32 90 900 do 39 0.32 900 Fairly Brig tAll Over andMuch 60 0.41

Improved in Appearance; few Dull Streaks. 120 32 0.41 120 24 0.41 10.1 200 20 0.41

(6) Roll dry with rubber rolls; and

(7) 1.0 second immersion in fused plating salts before electroplating with the aluminum-manganese alloy coating to bring the panel to about the bath temperature.

A fused salt electroplating bath was prepared from 80 parts aluminum chloride, -10 parts sodium chloride and 10 parts potassium chloride (by weight), and then anhydrous manganese chloride added thereto in varying amounts as necessary to give the percentages of manganese in the bath noted below in Table I. The bath was maintained at a temperature of about 625 F. Anodes of alu- .minum (ZS-F aluminum) were immersed in the electro- .lyte, and an anode-cathode spacing of about l /z" was used. The plating conditions and manganese concentra- Panels 9, 13, 23, 26, 28, 48, 53, 59, 61, 62, 64 and 67 were given standard Scotch tape adhesion tests. Panels 9 and 13 exhibited good adhesion, panel 23 very good adhesion and 26, 28, 48, 53, 59, 61, 62, 64 and 67 excellent adhesion.

EXAMPLE III Table 1r Description 0.10 lgzJitfi of electrodeposited zinc- I H 0. SQ-millionth's of an inch matte aluminum coating.

. coating.

fio-miilzlionthsoi an inch bright aluminum alloy coaing. -mill ionths of an inch bright aluminum alloy coatmg, BO-milliontbs of an mch bright. aluminum dbservations made during thetest included: 7 Q (1) Time required for white rust orstain to form (2) Type of coating protection .(a) sacrificial or barrier on the panel r ."(4)' Time required to produce sta esericoyerage by red I rust v v V I g The attack on the samples varied according to the type or protection given by therespective coating The data 7 i'collected appears below inT-able IlI. t

J Tdble 1 11.

r o. SO-millionths of an inch bright aluminum alloy' 3 Time. required for thenrn'signierreid rust reap ear aluminum are sacrificial. barrier protection given by the alloy coating indicate an extremely low porosity. Bright deposits of approximately-80% aluminum and %-manganese gave superior pro- 5 tection against red rust formation in the salt spray to all.

7 other coatings tested. r The following discussion lists for each class of coating:

T in.coarings;The 0.25 lb./BB tin deposits protected the steel by acting as a barrier coating. The first red rust formed at the pores and rapidly spread over the. panel. Only 2 hours were 'required to cover the panel with approximately 50% red rust.

Zinc c0atings.--Theelectrodeposited zinc coatings of 0.10 oz./ft. (85-millionths of an inch thickness) were covered with white rust at the first hour check. There was no red. rust until substantial areas of the base metal were exposed, which was first found at the 12 hour check. Once the red rusting had started, it increased very rapidly and at the 19 hour-check 5 0% of the panel was covered by red rust. I V

Matte aluminum coatingS.-The matte aluminum coatings'of 80-millionths'of an inch thickness acted as a sacrificial coating the same. as the zinc. However, the first ef- Then the coating beganto dissolve at the top section of the sample-whereitwas most affected 'by the salt spray. This action exposed large areas of the base metal and red rust began-tofo'rrn- As the coating was removed progressively down the panelgithe red. rust followed the removal S pattern. Thealurninurn deposits gave better protection thanthe zinc since there was no red rust found'on the panels coated aluminum until the 19 hour check. Fifty percent red rust. was found at the 36. hour check.

-. ANALYSIS OF SALIKSPRAY TEST DATA Coating... Hours to First. Thickness Sign oi:, Hours to .Hours to Hours to. Sample Type of inM' First.Red j 6% Red 10% Red Over Remarks No. Coating. liouthsof. ;.v Rust 7 Rust Rust Red Rust.

' anInch. .White. Stain p Rust...

. ..15 2 Barrier Coating. ..85 1 12 '19. sacrificial Protection. 85. 1. 12 .19 Do.

. ,7 v5 '7 12. 19. Barrier Coating. 15; M19 36 42 0.

.. .19 .36v sacrificial Coating. .80 36 42 I 49 .72 0. p 30. 42 Barrier Coating. ...80 D0.

80. 42 Do. 80. 72 D0.

1 Not Reached, 'llest Concldu: I i

The results of the'salt spray test on bright aluminum j manganese'alloy deposits indicate a remarkable corrosion:

resistance. For example, when comparedtoj an equivaw lent thickness of zinc, the-alloy failed to show red rust" for 72 hours, whereas, a similar thickness of zinc showed; red rust in 12.h0u'rs. The 85-millionths of an inchelectro,deposited-'zinc coatings have the second disadvantage.

of forming white rust within the first'hour in the test.

i For 0.2 5 -lb./BB tin" (IS-millionths of an inch thickness), red rust appears in less than 2' hours, whereas, for the 0.05 lb./BB .alloy coating (7-millionths" of an inch thickness) red rust occurs at 7 hours. An equivalent thickness of the alloy .(lS-millionths of an inch) showed no red rust until it was in the salt spray for 19 hours,

It was determined in the salt spray test that the clectrodeposits of tin and the alloy of aluminum and manganese T act as barrier coatings and the electrodeposits of zinc and 60 The' first eifect of the salt spray'test on the allow coating was to produce ablue orlight tan stain.- This stain-was ua un i s fi -str k ndfwas i generally a n cation as to where the .first redrust would form. The.

thinnerthe coating, the sooner; this stain -;forme'd. For 6 5:. example, the 15-millionths of an inch coatingstained in 57 hours. the 30-millionths of an inch'coating stained in 12 hours and all coatings over 60 -millionths of "an inch f stained sometime between 42 and'72'hours.

The formation of red rust was also a function of coat- 7( ing weight'up to the 60-mil1ionths of an inch coating. The 7-millionths: of an' inch coating showed rust in 5 hours; the- 15.-millionths of an inch showed rust in 19 hours and the 3.0-millionths 'of an inch showed red rust in 42 hours. All coatings'lof 60- and 80 -mi1lionths of an 75 The superior performance and 1 various observations noted fects of the. testwere observed as a graying of the coating.

inch varied between rust? at 72 hoursand no rust at 136 p 17 hours at which time the test was concluded. None of the panels plated with coatings over 60-millionths of an inch had 50% of their areas covered by red rust at the conclusion of the test.

What is claimed is:

1. A base material coated on at least a portion of its surface with an alloy consisting essentially of about 10- 70% manganese and the remainder aluminum together with incidental impurities.

2. A base material coated on at least a portion of its surface with an alloy of aluminum and manganese consisting essentially of about 16-30% manganese and the remainder aluminum together With incidental impurities.

3. A base material coated on at least a portion of its surface with an electrodeposited alloy of aluminum and manganese consisting essentially of about 10-70% manganese and the remainder aluminum together with incidental impurities.

4. A base material coated on at least a portion of its surface with an electrodeposited alloy of aluminum and manganese consisting essentially of about 16-30% manganese and about 84-70% aluminum together with incidental impurities, the alloy being bright as electrodeposited.

5. A ferrous metal base electroplated with an alloy consisting essentially of about 10-70% manganese and the remainder aluminum together with incidental impurities.

6. A ferrous metal base electroplated with an alloy consisting essentially of about 16-30% manganese and about 84-70% aluminum together with incidental impurities, the alloy being bright as electroplated.

7. A ferrous metal base coated on at least a portion of its surface with an alloy consisting essentially of about 10-70% manganese and the remainder aluminum together with incidental impurities.

8. A ferrous metal base coated on at least a portion of its surface with an alloy consisting essentially of about 16-30% manganese and the remainder aluminum together with incidental impurities.

References Cited in the file of this patent UNITED STATES PATENTS 1,027,495 McNitt May 28, 1912 1,236,383 Fahrenwald Aug. 7, 1917 1,256,084 Watkins Feb. 12, 1918 1,426,507 Rodrian Aug. 22, 1922 1,464,625 Pacy Aug. 14, 1923 1,795,512 Schmidt Mar. 10, 1931 1,830,142 Taylor Nov. 3, 1931 1,974,970 Nock Sept. 25, 1934 2,013,926 Pacy Sept. 10, 1935 2,149,656 Armstrong Mar. 7, 1939 2,745,172 Townsend May 15, 1956 2,762,764 Owen Sept. 11, 1956 2,807,575 Charlton Sept. 24, 1957 3,018,194 Norman et a1. Ian. 23, 1962 FOREIGN PATENTS 568,903 Belgium Dec. 2, 1960 OTHER REFERENCES Gittings et al.: Article in Trans. ASM, vol. 43 (1951), pages 587-610.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,167, 403 January 26 1965 Edwin J. Smith et al.,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 23, for "15 depending" read l5, depending line 37, for "where special" read where a special column 15, Table II, second column, line 3 thereof, for "89millionths" read 80-millionths same column, Table III, ninth column, line 8 thereof, for "145"?v read- 393F145 (1) same Table, same column, lines 9, l0 and 11 thereof, for

each occurrence, read same Table, eighth column, line 11 thereof, for "186" read 186 Same Table, Same column line 12 thereof, for read same Table,

seventh column, line 12 thereof, for "186" read 186 same Table, same column, lines l3, l4 and 15 thereof, for

"( each occurrence, read same Table, sixth column, line 15 thereof, for "145" read 145 same Table, same column, lines 16 and 17 thereof, for '1 each occurrence, read same Table III footnote thereof,

for Not Reached, Test Concld," read Not Reached.

Test Concld.

Signed and sealed this 29th day of June 1965,,

' (SEAL) Attest:

ERNEST W. SWIDER EDWARD J, BRENNER Attesting Officer Commissioner of Patents

Claims (1)

1. 7. A FERROUS METAL BASE COATED ON AT LEAST A PORTION OF ITS SURFACE WITH AN ALLOY CONSISTING ESSENTIALLY OF ABOUT 10-70% MANGANESE AND THE REMAINDER ALUMINUM TOGETHER WITH INCIDENTAL IMPURITIES.

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