The Monthly Review

Published Monthly by the American Electroplaters Society

A Society for the Advancement of the Science of Electroplating

Volume XVI January, 1929 No. 1

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EDITORIAL

The officers of branches and members, as well as the National officers, are going to be tested again this year, for prudence, wisdom and patriotism as well as unselfishness, for which this Society is noted.

There has never in the history of our industry been so much need of intensive research in plating problems as there is at present, and it behooves this Society as a whole to give much thought to the further continuance and extending of our fellowship at the Bureau of Standards at Washington, D. C., under direction of Or. W. Blum.

With new President of United States of America taking helm of the Ship and perchance many new Cabinet officers, many of them are not familiar with our efforts. It will be a matter of study and much thought and hope that progress at the Bureau will continue and it may be the opportune time to approach your employer to subscribe to our Research Fund if he has not already done so, and if he has to try and get at least one new firm to assist in the worthy work this year.

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ELECTROPLATING ON ALUMINUM ALLOYS

Copy from Convention Proceedings

By Harold K. Work: Abstract
(Member Pittsburgh-Branch, A. E. S.)

Electroplates of most metals on smooth aluminium surfaces are of doubtful value unless heat treated. Plating on a roughened surface is recommended as being a practicable procedure. Methods of plating the common alloys are given. A dip is described for commercially pure aluminum which roughens the aluminum and simultaneously forms an immersion layer on the surface. For alloys containing a cutectic network a dip which attacks one constituent of the network is ‘advised. Where the strong alloys are plated an excellent product is easily obtained providing the’ alloy has been subjected to the usual heat treatment, as is customary for these alloys to develop their strength.

“Introduction. With the increasing use of aluminum in recent years there has been an ever growing demand for methods of plating on it. Many such methods have appeared in the literature but few of them have net with commercial success.”

“The difficulty with most of these processes has been that, while the deposits have an excellent superficial appearance when new, they blister and peel after short service in the presence of moisture. Another difficulty has arisen from the disregard of the composition of the alloy being coated. This, no doubt, has resulted from the popular use of the term ‘aluminum’ to designate the alloys as well as the commercially pure metal. Yet it could hardly be expected that one method of plating would give equally good results for the commercially pure metal and also for alloys containing large amounts of either copper or silicon. Another factor which has been generally overlooked is the condition of the metal in plating on the strong alloys. These alloys show different degrees of inherent corrosion resistance, depending on whether the metal is annealed, hard rolled, or heat treated.

“To make a broad study of electro-plating on aluminum and its alloys, the Aluminum Company of America established an industrial fellowship at Mellon Institute of Industrial Research in 1925. A summary of the results of this research follows. The writer is indebted to Dr. E. Ward Tillotson, assistant director of Mellon Institute, and to Dr. Francis C. Frary, research director of the Aluminum Company of America, for helpful advice during the progress of the experimental work.

“Principles Involved. Some of the reasons advanced in the literature for the difficulty in plating on aluminum are as follows:

1. Presence of an oxide coating on the metal.
2. High position of aluminum in the electro-motive series.
3. Presence of gas, such as hydrogen, either in the electroplate or in the aluminum.
4. Failure of the aluminum to alloy with the coating metal.
5. Attack of the aluminum by acids or bases in the electrolyte.
6. Action of impurities in the aluminum.
7. Presence of pin holes in the coat that allow subsequent corrosion.
8. Difference in coefficients of expansion of aluminum and the coating metal.
9. Presence of chemicals from the solution in the pores of the metal.
10. Tension in the coating metal.

“By analogy with other examples of electro-plating which are successful, most of these explanations lose weight. Two of them, however, cannot be so readily disregarded. These are the oxide film and the high position of aluminum in the electromotive series.

“The oxides at the surface must be removed in plating on any metal if the coating is to adhere. Aluminum has a greater tendency to form an oxide coating than most other metals which are plated. As a result it is not surprising that the failure of deposits to adhere to it is often ascribed to this oxide film on the surface. Ledin, Burgess, and others have relied on halogen acids to remove it. Szarvasy advises non-aqueous solvents in the bath used for applying the first layer. Betts fuses the first layer onto the aluminum. Most other investigators advocate a step in their processes for the removal of this oxide.

“The second difficulty, the high position of aluminum in the electromotive series, introduces two possible problems in plating. It may cause deposition of a non-adherent metal layer at the start of plating and thus prevent the deposit from adhering, or, when plated with a metal far below aluminum in the electromotive series, may accelerate corrosion so much as to make the product worthless. This deposition by immersion would be similar to the action of zinc, as has been considered by M. R. Thompson. Aluminum presents the same problem but to a less extent because of its passivity. Lodyguine uses a bath of low metal content, ion content, to avoid this deposition by immersion.

“Many investigators recommend the application of a high potential for a short time at the start of plating and then proceed at the required voltage. This temporary high potential overcomes the tendency for deposition by immersion. Others suggest the use of a dip bath that gives an adherent coat by immersion and then electro-plating over this layer. Ledin employs cadmium, Ryan and others use mercury, and Creswick and Shaw specify tin. This type of pro-cedure is common and becomes an advantage when properly utilized, as is discussed later. For nickel plating, baths of low acidity or free from chlorides are recommended to keep the aluminum passive and to prevent deposition by immersion, as well as the addition of materials to increase the cathode polarization of the bath.

“The other aspect of the high position in the electromotive series, namely, the lack of corrosion resistance of the product, does not allow so many remedies. Guillet and Gasnier advise the use of alternate layers of nickel, copper and nickel to secure a heavy and impervious deposit that resists corrosion.

“In consequence of these difficulties in plating on aluminum, procedures are recommended which are not commonly used for plating on other metals. Travers, D’Amico, Martin, Mason, Mix and Genest, Pucillo, Baille, and others recommend heat treatment after plating to improve the deposit. Roughening of the metal surface to get mechanical adhesion is another device that is advised. Canad uses an iron and hydrochloric acid dip to obtain an electrolytic etch. Maxuir substitutes manganese for the iron. Desch and Vallan aid their etching by means of current. Murset uses caustic for etching. Guillet and Gasnier roughen the surface by means of a sand blast. Such procedures of etching and sand blasting both serve the double purpose of removing oxide and roughening the surface. Reports vary as to the success of these processes, no doubt due to differences in operation.

“Alloys Considered. A group of the most commonly used aluminum alloys was selected for tests of plating methods. These alloys are based on commercially pure aluminum, which contains 99.0 to 99.4 per cent of aluminum, the remainder consisting mainly of iron, silicon, and copper introduced in the production of the metal. The metal of this composition is termed 2S. The composition of the alloys tested is given in Table I.

“Testing on Deposits. Adhesion. Adhesion is tested by bending the specimens sharply if they are soft, or breaking them if they are hard, and observing the behavior of the plate. A poor plate pulls away from the aluminum.

“Corrosion Resistance. Corrosion resistance is determined by four methods. They consist in subjecting the specimens to partial immersion in salt solutions, to water vapor, the outdoor atmosphere, and to actual service. The partial immersion in salt solutions perhaps requires explanation in view of the many methods available for such accelerated corrosion tests. The test is made by immersing the lower halves of the specimens in a solution containing one per cent each of sodium and calcium chlorides,

“This test allows a large number of specimens to be tested for prolonged periods with a minimum of equipment, That it makes a distinction between the corrosion in different areas, aids in the prediction of the nature of the corrosion in the atmosphere, Blistering and peeling usually occur in the immersed portions, while pitting is more pronounced above the solution line, The corrosion below the solution line is generally indicative of rapid failure on outdoor exposure, The test is valuable from a strictly qualitative standpoint. The exposure to-water vapor test gives results resembling those observable on outdoor exposure, but avoids dirt contamination of the specimens, thus facilitating examination.

“Table I. Percentage additions to commercial aluminum to form alloys. The strong alloys may be obtained in different conditions which affect the plating. These conditions are indicated by symbols, as 0, soft annealed. H, strain hardened after rolling. W, heat treated and quenched to improve strength. T, heat treated, quenched and aged to develop the maximum strength.

“Cleaning Procedures. Organic Solvents (O.S.) Benzene, naphtha, or carbon tetrachloride may be used to remove excessive grease from the metal surface. The use of such a solvent is not always necessary, but is very effective, especially for removing buffing greases before an acid dip.

“Mild Alkaline Cleaners ( M.A.) . Very dilute caustic soda, mixtures of sodium carbonate and bicarbonate, or commercial cleaners for aluminum are also used as grease removers with the additional advantage that they slightly attack the metal surface and make it more susceptible to the action of other solutions. The following is a good example: sodium carbonate, 22.5 g/L. (3 oz. 3/4 gal.); sodium bicarbonate 45 g. 3/4 L. (6 oz. 3/4 gal.). This cleaner is used hot at a temperature of 93° C. (200° F.).

“Acid Cleaners (A.C). Hydrofluoric acid is a very effective cleaner. A satisfactory solution contains 1 part of 48 to 52 per cent hydrofluoric acid to 9 parts water. Although this particular solution will not take off heavy grease, it will at least remove small amounts left by fingerprints, etc. It is slightly superior to hydrochloric acid, probably because of its action-on silicon, but the latter acid may sometimes be substituted for it. The metal is usually dipped in it from ten to sixty seconds. This treatment produces an active surface.

“Dilute Mixed Acids (D.M.A.). Dilute hydrofluoric-nitric acid mixtures are often very effective, where a slower attack is desired. A satisfactory combination is made by substituting nitric acid for one-half of the hydrofluoric acid in the preceding dip.
“Concentrated Mixed Acids (C. M. A.). Concentrated hydrofluoric-nitric acid mixtures are sometimes used to whiten the metal surface, although more often to roughen it and will be discussed later.

“Passive Dips (P.D.). Nitric acid may also be used to whiten the metal surface and make it less active. It is, in addition, of value for stripping deposits.

“Pumice Scrub (P.S.). Scrubbing with pumice can be used prior to dipping in some of the solutions which roughen the surface before plating.

“Brushing (B.). Washing with a soft brush and water will often remove non-adherent particles before plating, and thereby make possible the formation of a smoother deposit. This procedure is advised whenever such particles are present.

“Plating on a Smooth Surface. Following the common practice in plating on smooth surfaces of other metals, attempts were made at the beginning of this study to plate on relatively smooth aluminum surfaces. For this purpose many solutions were tried. The results show that acid baths gave non-adherent plates, while cyanide baths usually yield blistered ones. Of all the solutions investigated the cyanide-zinc baths give the best deposits, and accordingly zinc was chosen for use as a preparatory coating. Most of these cyanide-zinc baths, however, are so alkaline that they attack the aluminum. To remedy this defect, ammonia is substituted for the caustic soda in them.

“Further experimentation showed that an addition agent is also conducive to better results. Three such agents are successful; namely, gum arabic, peptone, and gelatin. Of these, gelatin is the most reliable, and is used in amounts up to 5 g./L. (0.6/ oz./gal. ) . This relatively large quantity gives a solution that changes only slowly in service. A satisfactory bath has the following formula:

“This bath is used cold at a current density of 0.5 amp./sq. dm. (4.5 amp./sq. ft.). A five-minute plate, or its equivalent at other currents serves as a foundation for plates or other metals. Nickel, copper, cadmium, and brass have all been applied over this zinc layer. The resulting deposits are of excellent appearance, adhere well, can be soldered, but fail rapidly in the corrosion tests. The nickel usually peels, while the softer metals blister on exposure to moisture or salt solutions. Deposits of 0.013 mm. (0.005 in.) rarely last a day in the salt tests, and only two or three months on outdoor exposure.

“However, plates on objects such as pen holders and letter openers, which were subjected to dry indoor service, are in good condition after almost two years. The application of lacquer helps to protect such plates. Except where zinc alone is used as the coat, these plates are of value for only very mild service. It is possible nevertheless to make them much more resistant to corrosion by a heat treatment. Where this heat treatment is used, copper is applied over the zinc layer from a cyanide bath and then the object is subjected to heat. A copper bath that can be recommended for this application is as follows:

“After a short time the plating may be finished in an acid copper bath if desired. The use of cadmium, nickel or brass, instead of the copper, over the zinc proves unsatisfactory when the heat treatment is used. In Fig. 1 (in pamphlet) is shown the effect of heat treatment on the corrosion resistance in salt solutions. To ensure this greater corrosion resistance in the process, alloying of the coat with the base-metal appears necessary. Such a method is applicable to every alloy that has been studied. Figs. 2, 3 and 4 (in pamphlet) illustrate the alloying action at the temperature of the heat treatment used to develop the strength of the strong alloys.

“The heat treatment is easily accomplished in a muffle’ furnace, or in a nitrate bath. A temperature of 430° C. (806° F.) in a muffle for thirty minutes is sufficient to cause alloying when 2S is coated. With lower ‘ temperatures a longer time should be used, but any temperature below 330° C. (626° F.) requires an excessively long time of heat treatment. With the strong alloys it is advisable to combine the usual heat treatment to develop the strength with the treatment that makes the plate adhere. The following are the steps in the procedure for obtaining a nickel plate on aluminum: zinc plate, copper plate, heat treat, buff, and nickel plate. This order gives a better finish than if the nickel is applied before the heat treatment. This result is due, no doubt, to the fact that solution is included in the pores of the copper plate, and, on being expelled, roughens the surface.

“The process has limitations but is included here for the application it does have. The major objections to it are as follows: ( 1 ) The heat treatment anneals the widely used 2S and 3S alloys; (2) The heating is an added expense; (3) Large objects buckle during heating; (4) Copper accelerates the corrosion of the aluminum and causes more rapid pitting, where nickel is ;the final coating.

“The process described in U. S. Patent 1,256,954 of Travers is of interest here because it includes a heat treatment. The ‘aluminum is plated directly with nickel and heat treated at 240° C. This low temperature is used to avoid annealing of the aluminum. The process was tested by the author and found to have merit when the heat treatment was long enough. Ten or more hours in a muffle was sufficient to make adherent and corrosion resistant plates on 2S. With less tine the deposit did not always adhere after plating and blistered in salt solutions.

“It is realized, however, that this time might be reduced by improvements in the technic of plating. Examination of specimens claimed to be plated by the process showed no visible alloying of the nickel with the aluminum. This method is subject to some of the objections of the previous one. There is the expense of heat treatment, buckling of large objects, and, unless the time of heat treatment can be reduced, a slight annealing action that softens the aluminum somewhat.

“As a result of these tests, as well as trials of other processes described in the literature, the author has come to the conclusion that most plates on a smooth aluminum surface are to be.-viewed with doubt as to their commercial utility, unless they have been heat treated.

“Plating on a Rough Surface. Canac reported that aluminum could be nickel plated if the surface had been roughened. He used a hydrochloric acid dip with a small amount of iron in it. The objection has been raised to this process that it is not applicable to all alloys, and so Guillet and Gasnier advised sand blasting- to roughen the surface. In this process it is not possible to build up a heavy enough deposit of nickel to resist corrosion without peeling, and therefore layers of nickel, copper, and nickel have been suggested.

“Tests have been made on the use of the sand blast indicating that the process involving sand blasting would probably be successful if the correct fineness of sand and the proper air pressure were chosen for the particular alloy. Objections to this process are found in the equipment required, and in the introduction of another color of metal, which appears on wearing, by the copper layer which is used to prevent peeling when nickel is the desired coating.

“For the average plating shop chemical etching is therefore more suitable. The assistance of an electric current in the etching has been considered, but is superfluous.

“Etching solutions which have given the best results may be divided into three general classes, as follows: (1) Acid dips with high metal content; (2) Acid dips with low metal content; (3) Acid dips without added metal. Each of these groups has certain characteristics that make it particularly effective for certain of the alloys. A few of the typical examples of each group are shown in Table II.

“The high metal dip differs from the other dips in that the roughening of the metal is accompanied by the formation on the aluminium of an immersion layer surface. This layer greatly facilitates plating. The dip accomplishes some of the roughening by attacking through the pores of the immersion layer. When pits are formed they are quite large, and often’ undercut with smooth areas between them. This makes an excellent anchor for holding the plate on the aluminum. Deposits as thick as 0.38 mm. (0.015 in.) have been applied in 2SO aluminum, and on bending the nickel broke in small pieces rather than flaked off. The dip also does not require close control, for relatively large changes, as much as 20 per cent sometimes, in the time of dip or in the composition of the solution do not greatly reduce the effectiveness of the dip. Occasionally, however, acid and nickel chloride must be added to maintain the original proportions. Titration is employed to control the acidity, and colorimetric methods may be used for the nickel content. Copper impurities in the nickel chloride may cause the nickel immersion deposit to be dark when the dip is new, but this discoloration will work out in time. Adding at first a few scraps of aluminum, to the dip speeds up the removal of the copper. This type of dip has one serious fault. It cannot be used for all of the alloys. Even small amounts of alloying materials usually cause it to produce inferior plates. The procedure is limited, therefore, mainly to use for 2S aluminum.

“The low metal content dips are probably the most generally applicable to all types of alloys, but they do not give as satisfactory results as other dips for 2S and alloy with a eutectic structure. The roughening action is not quite as good as that obtained with the high metal dip, and the absence of the metal layer after dipping is a disadvantage in plating. This type of dip finds its greatest application on those alloys which are inherently most resistant to corrosion and consequently require least roughening to anchor the coats.

“In general, the actions of the nickel, iron, and manganese dips are much the same. There are, however, slight differences that deserve mention. Where articles are being dipped in very rapid succession the nickel dip tends to heat up, begins to act on the aluminum more rapidly, and gradually loses its green color by precipitation of the nickel. On standing for a time the nickel redissolves and the dip again operates satisfactorily. The iron dip behaves similarly, though to a less extent. The manganese dip is even less’ affected In addition, the manganese dip maybe used for 3S alloy and obviously, has the advantage of the widest application.

“The acid dip, which has been used commercially, was next studied and its particular application found in such alloys as have a eutectic network structure. The mixture of nitric and hydrofluoric’ acids attacks quite rapidly the constituent in the network containing the least aluminium and leaves the high aluminum part. This gives an excellent roughening where the network is fine, as in the case of die castings; but where there is a large enough amount of the alloying material it may even be used where the structure is coarse, as in some of the sand castings.

“Roughening Procedures. 2S Aluminum. This may be plated after roughening with either the high metal content dip or the low metal content dips, but the former is more satisfactory. This is particularly true when objects have been formed into irregular shapes. For this reason a 60-second dip in Ni 1 dip is advised as being most satisfactory, although the following have given fair results in the other dips: Mn 1, 40 sec.; Ni 2, 60 sec.; Fe 1, 30 sec. This high metal dip is one of the simplest to operate. The only time that it is at all likely to fail is when the article is made from very hard rolled material. Fig. 5 shows the etching action obtained by its operation.

“3S Aluminum. The high metal content dip, successful for plating on 2S aluminum, proves undesirable for this alloy. It does produce a coat of satisfactory superficial appearance, but the plate peels off rapidly on exposure to salt solutions or to the outdoor atmosphere. For better results on this alloy, the low metal content dips may be used except that the iron and nickel ones unduly roughen the surface. From all standpoints, consequently, the manganese dip (of 15 to 20 seconds) is most satisfactory. This is explained no doubt by the fact that the manganese in the metal assists that in the dip to give a fine and uniform etch. Fig. 6 (in the pamphlet) shows how the etching takes place.

“Strong Alloys. In general the low metal content dips are best suited for plating on the strong alloys. It is possible, however, to obtain good deposits on some of these alloys with the high metal dips, as well, although with these the plates are less reliable, especially for manufactured objects. This is perhaps due to the lack of uniformity in the heat treatment of the manufactured articles. But regardless of which type of dip is used with these alloys it is the condition of the metal that is of more significance than the plating procedure itself. This is true because the value of the plate parallels the corrosion resistance of the metal coated. For instance, no nickel plate has been obtained on 17 SH that does not peel on exposure to salt solutions or to the outdoor atmosphere, except when the metal is so severely etched that it is disfigured. Plates can be obtained on the metal in the T condition, however, that resist salt solutions for many weeks with no appreciable corrosion. Briefly, the dips that have been successfully used for these strong alloys are shown in Table III.

“Die Castings. For the die casting alloys, 13, 73, 83, 85, and 93, the roughening of the surface, so necessary for successful plating, is easily accomplished by the acid dip This removes one constituent of the eutectic network, leaving an excellent surface for plating. A dip of thirty seconds is advised for this action on all the die castings, but the time may be varied considerably and still produce satisfactory results. The proportions of the acids used may also be widely varied without decreasing the effectiveness of the dip. Fig. 7 and 8 (in pamphlet) are interesting pictures of the roughening action.

“Sand Castings. Three typical sand casting alloys have been plated. No. 47 consists of a combination of areas resembling 2S and areas like die castings. The procedure for die castings is followed but a longer dip (90 seconds) is necessary for complete adhesion. Fig. 9 shows the roughening that occurs on this alloy. No. 112, on the other hand, has quite a different structure. The zones in it that are rich in the alloying constituent cut the surface only at infrequent intervals. Attack of even these limited areas by a two-minute acid dip, however, gives sufficient pits to hold the plate on well enough for any mild service. That is, a nickel plate of 0.013 mm. (0.0005 in.) begins to fail after about seven days in salt solution. This is, of course, inferior to most of the other plates under discussion. Fig. 10 indicates that the surface is not greatly roughened. Alloy T. 195 does not have enough areas cutting the surface to allow use of the acid dip at all. Since, however, it resembles 17 ST, the same type of dip as is used for the strong alloy was tried successfully. Fig. 11 (in pamphlet) shows that the surface is not greatly roughened and yet the product is corrosion resistant.

“Plating Procedure. When the surface has been first roughened, nickel appears to be the most workable metal for the foundation coat. However, selection of the bath that produces this coat is, strange to say, of minor importance, since almost any nickel bath will give a satisfactory deposit if correctly used. Various ones can therefore be recommended for use on aluminum; neutral baths, chloride-free baths, and baths with a material added to increase the cathode polarization. This subject has been discussed above in the section entitled ‘Principles Involved.’ In general, any nickel bath that operates satisfactorily for zinc is acceptable for use on aluminum. Three recommendations are given in Table IV.

“The first two of these solutions are well known The third one was recommended by George B. Hogaboom. It gives excellent deposits that are white even in the recesses of profiled objects. The second solution is often modified by the substitution of double nickel salts for part of the single salts. All three may be further modified to use under a wide variety of conditions, but the following are recommended as good starting points.

“The application of a high potential at the start of plating is beneficial for some alloys, but not absolutely necessary. A moving cathode rod allows faster plating. pH 6 gives good results.

“Processes Recommended. Although the plating processes have already been indicated under various headings, this section serves to segregate the individual steps of the complete procedure in a skeleton outline, and also presents a tabular summary of results in Table V. A previous section of this paper on cleaning procedures explains the abbreviations used.

“Skeleton Outline of Typical Plating Procedure:

1. *Remove grease (M.A.) (O.S.) (P.S.).
2. Rinse with clear cold water.
3. Make surface uniform (A.C.) (P.D.).
4. Rinse with clear cold water.
5. Roughen surface.
6. Brush off adhering particles or dissolve dark metal stains (B.) or (P.D.) (optional).
7. Rinse with clear cold water.
8. Plate first layer with most suitable metal.

*Frequently steps 1 and 3 may be combined.

 

“Again it must be remembered that almost innumerable variations in these procedures are possible, but a summary of one successful process for each alloy is presented here for guidance.

“It can be assumed that the unplated specimens used are reasonably free from grease, except the castings alloys, which are polished.

“When adopting these procedures for use, it must be borne in mind that the dipping is the important step. The most suitable time of dip has to be determined for each particular application. The above figures are useful guides but no more. They must be revised each time they are used to correct for variations in the temperature of the dip, the purity of the chemicals, and the degree of passivity of the aluminum surface. Every attempt to apply the procedures for the first time must always be accompanied by both adhesion and corrosion tests.

“In some plating work where large articles must be immersed, it may be found that the time of dip is too brief to permit uniform attack of the top and bottom of the objects. Under these circumstances the dip must be diluted and a longer time of dipping employed.

“Properties of Deposits. The adhesion and accelerated corrosion tests referred to previously in this paper, are presented collectively in Table VI. The plate under discussion is 0.013 mm. (0.005 in.) thick.

“It will be noticed from Table VI that some of the alloys show good corrosion resistance even with poor adhesion. This is probably explained by the inherent corrosion resistance of the alloy. With most of the alloys, however, it is necessary to have good adhesion in order to secure good corrosion resistance.

“It may also be stated that the outdoor exposure tests on the specimens are even more favorable than the accelerated corrosion tests. Such exposure tests of six months to one year in duration on specimens of nickel plated 2S, 17 ST, and die castings indicate excellent corrosion resistance. Even where a few spots of oxide have appeared on the surface, the wind and rain have removed them. The explanation is, no doubt, that the aluminum becomes passive.

“Advantages of Plated Aluminum. Aluminum has the valuable characteristics of lightness, ease of fabrication, and conductivity. The plated product acquires the additional advantages of improved appearance and increased resistance to abrasion.

“The improvement in appearance from the natural color of the uncoated metal to a nickel finish makes it applicable whenever uniformity of metal color is desirable. This is especially useful in the field of plated automobile fixtures. The increased resistance to abrasion makes it valuable whenever the dark smudges rubbed off aluminum by friction are objectionable. This is especially true for articles that come in constant contact with the hands.

“Nickel is the metal most frequently used as a coating for the aluminum, and it is fortunate that the two metals are so nearly the same color.

“This fact makes worn spots in the nickel less perceptible than when other metals are nickel plated. Also in contrast to iron the corrosion products are white and easily removed.

“The micrographs in this paper were furnished by E. H. Dix, Jr., of the Aluminum Company of America.” (Applause.)

Chairman Smith: Does any gentleman wish to ask Mr. Work any questions?

Mr. Dan Wittig (Milwaukee): In plating all this aluminum you must know just exactly what you have before you start, what dips to use, etc. If you don’t know the composition of the metal you couldn’t do it successfully.

Mr. Work: Up to a certain point it is right. For instance, die castings, the same methods were used for all die castings, and in general you know what die castings are. All the sand castings I have plated so far have been plated by the one metal. There is one particular sand casting alloy which is heat treated. It is best to be very cautious with some of the alloys, for instance, they put in a small amount of copper in some of them, a per cent and a half, or something like that, to increase the strength. You cannot go ahead as if it were pure metal.

Mr. Ter Doeste: I would like to ask the gentleman the nature of that salt solution test.

Mr. Work: The salt solution test I use most generally consists of just taking a beaker of salt solution containing one per cent of sodium chloride and one per cent of calcium chloride and emersing the specimen half way.

It is very convenient for laboratory work where I plated a large number of specimens, for instance, the salt spray test is rather cumbersome, if you want to test a lot of specimens for a long time and we have outdoor exposure tests, some of them are on the boards I passed out.

Question: Did the speaker mention the method of cleaning buffing compounds, etc.?

Mr. Work: That depends on the condition you get things in. Most of the specimens I receive are flat sheet that doesn’t require much cleaning. In fact, a great many I had made it necessary only to dip in hydrofluoric acid. A ten per cent solution would clean them up nicely, so I didn’t have to use much to remove buffing greases. Where I did have to remove buffing greases, either carbon tetrachloride or benzine or mild cleaners were used. I didn’t make a study of the thing to find out absolutely what was the best one to use. It is up to the man who is plating, anyway.

Question: Are these highly polished surfaces hydrofluoric acid treated ?

Mr. Work: Yes, just a short dip, ten or fifteen seconds. The dip that is.

Question: Is that the iron dip?

Mr. Work: I haven’t used the iron much. As I said, because I found manganese was pretty much the same and the manganese would work for the 3S alloy when the iron dip wouldn’t otherwise for a whole lot of the alloys. Here is something that might answer your question. Here is a specimen that is just as it can from the nickel bath, grey looking, but it is quite smooth and could be buffed on a single wheel.

Question: Do you recommend the use, then of this hydrofluoric or manganese dips? That is for die castings?

Mr. Work: No, it is nitrate Plating aluminium seems to be a cleaning problem. of hydrofluoric acid.

Member: Will you outline the method of cleaning from start to finish which you have found the most successful. I know it varies with the alloys but the method of cleaning from start to finish, what have you found the most successful?

Mr. Work: The one I use the most; first I clean with a mixture of sodium carbonate and bicarbonate, with or without the use of current; it can be used as an electric cleaner very satisfactorily. Then after the cleaning with alkali cleaner there is usually found advisable to give it a short dip in hydrofluoric, depending on what you are doing. The shorter the dip the more convenient it is to operate. You can usually get by with quite a short dip.

Member: If you use the nitrogen hydrofluoric what are the proportions ?

Mr. Work: Three parts of nitrate and one hydrofluoric.
Chairman Smith: If there are no other questions we will adjourn until nine-thirty in the morning.

(The meeting adjourned at eleven-thirty.)

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SOME EXPERIENCES WITH CHROMIUM PLATING

(Copy from Convention Proceedings)

Paper by S. T. Lunbeck, Philadelphia Branch

Mr. S. T. Lunbeck: “Foreword. Before reading this article I wish to call to your attention that I have purposely avoided any reference to the chromium bath as we are working under the Crodon process which is patented, but I don’t think they have any patents on the plater’s ingenuity. This article is presented to give an insight to the man who has not yet done chromium plating, the man who is doing it has already found out something.

“The plater of today is confronted with many new problems and finishes that necessitate the forsaking of old hit-and-miss methods and the majority of the trade, both young and old, are delving into chemistry and learning some of the mysteries of the where and why of certain chemical actions.

“Science has taught us that certain elements have definite purposes and by proper handling can be made to perform certain evolutions repeatedly.

“The all absorbing topic of chromium plating has brought forth many new problems. The deposition of chromium while similar to the deposition of other metals has peculiarities that no other solution has, high density, lack of throwing power, the radical action of the chromic acid on non-ferrous metals, the unusual high current required to deposit under certain conditions requires considerable thought and at times ingenuity.

“Stepping away from the nickel plating to chromium presents quite a contrast when one has been used to wiring numerous parts on a light gauge wire, for instance twenty valve spindles on No. 20 gauge wire, or twenty nozzles such as this on a light rack, then to find that two or three spindles on the same wire in a chromium solution would burn off immediately or that a rack such as this would be required to handle eight nozzles, then one gets a little idea of what a vast difference there is.

“Then each article requires a study as to the proper method of wiring or racking, many little details that one would never imagine could be so important creep in to keep one guessing. The violent gassing at cathodes requires special manipulations to avoid a gas pocket which will spoil an otherwise perfectly good job.

“Sometimes it is like a grab bag game the first time you do a new job you wonder what you have and are all anxiety when you take it from the tank; if O.K. you are highly elated; if not, down goes your pride and you begin to study a better method.

“The many factors that enter into chromium plating are immensely interesting, as well as vexing. Cleaning, strange to say, is of minor importance as compared to other deposits; in fact, many parts can be plated just as well- without any cleaning, -as if cleaned, in the usual way, this under some conditions, is quite an advantage, but is a practice I would not want to recommend as infallible. Cleaning in the regular way or electric cleaning with direct and reverse current, rinse in clear water, then in a weak acid dip consisting of one part H₂SO₄ to nine parts H₂O, rinse in warm water about bath temperature is a help although not a necessity, place in chromium bath and plate. The temperature is quite important, and should be carefully controlled.

“Voltage and amperage as usual are governed by the class of work to be plated, and the finish desired, plus considerable experience. Here, also, one gets quite a contrast to nickel where the usual load for same size tank would probably record two volts, 300 amperes, the result would be nearer five volts, 2,500 amperes, hence the necessity for the heavier wire and racks.

“After plating the desired time, take from bath, you will find a beautiful golden lacquer effect. It is advantageous to have a rinse tank adjoining the bath as the carry out is considerable and this first rinse water can be returned to the bath to an advantage. Rinse in clear water and hang in hot water as long as convenient to soak out the chromic acid, as this is hard to remove from deep recesses.

“There is considerable room for discussion as to what is the right procedure in chromium plating, whether on base metal or on a deposit of nickel. In some recent tests made it would seem that deposited over nickel was superior for instance, two valves were plated, one chromium for thirty minutes on the brass, the other nickel for thirty minutes, then chromium seven minutes. Under salt spray test the thirty minute deposit on brass began to break down after eighty-five hours, and continued up to end of one hundred and fifty hour test, the photo of valve showed the appearance of crumbling. The nickel plated valve stood the one hundred and fifty hours without any trace of crumbling, the plate showing a surface scratch but no corrosion.

“The finishing of articles before chromium plating is highly essential, what would pass for a first-class job in nickel would not pass- as a second in chromium, porosity wheel marks, chafing, and such defects are much more visible than would be with nickel.

“This presents a different line of handling from the ordinary, piling in tote boxes, as is customary, would be serious to a chromium job, hence more care in handling than is usual, fewer lines, more care in hanging in and removing and rinsing.

“The final finish or color buffing is required for a perfectly satisfactory job. -While many parts can be brought from the bath by proper handling of temperature and current that will not require a wheel finish, many more cannot, although these require little more than for a bright nickel. Any rejects may be easily refinished by stripping in a ten per cent solution HCl, neutralizing and recoloring.

“I might add that chromium plating is not a cure-all; it is not a rust-proof process, as some seem to think. While it is extremely hard, it will scratch, the base metal seems to govern the hardness. Urinal and closet fixtures due to medicinal and chemical mixtures are hard hit. Some of the sanitary cleaners for marble and porcelain cleaning are very detrimental to chromium plate.” (Applause.)

I would ask, Mr. Chairman, what the average voltage is you require on that.

Mr. Lunbeck: About five volts on the average run. I would also like to state in this case if I have failed to tell you anything, kindly hang it on the chromium corporation, and not on me. I would like to tell you the little I know but we are working under the licensee process and I am tied up, so I can’t reveal anything definite.

Mr. Musick: The Prize Awards Committee would like to know if you have done all this work under the license process and you are not in position to divulge (interrupted).

Mr. Lunbeck: I am very sorry. I know more than I am at liberty to tell.

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A. E. S. PAGE

Assembled Expert Scraps
With and Without Significance

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Isn’t It So? No man is good enough not to be better.
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A man who is clever enough to be boss at home is also wise enough not to brag about it.
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Where there is smoke, nowadays, there must be women.
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The less a man knows the longer it takes him to find it out.
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One way to make time seem shorter between paydays is to have the car installments due on the same days.
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Marriage is the most important thing in a girl’s life —until she has accomplished it.
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A man doesn’t have to plead insanity when he kills time; his condition is admitted.
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It’s hard to keep a bright person in the dark.
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The only things cheap now are talk and human life.
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Blessed are the peacemakers. They never need worry about being out of a job.
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Explaining Johnny’s absence. The following note was received by a teacher: “Please excuse Johnny for being absent yesterday. Through no fault of his he has a new baby brother.”— B. Pickars.
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“Make a sentence with the word ‘fortify’ in it.”
“I paid fortify dollars for this suit.”
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The Bigger Loss—
Three Scotchmen, McDougal, McPherson and McHenry, were chums in the trenches.
One evening a shell burst over them and blew McHenry’s head off.
“McDougal,” shouted McPherson, “McHenry lost his head.”
McPherson in great excitement asked: “What are ye saying ? McHenry lost his head? Where did it go to ?”
“What difference does it make? It’s game,” answered McDougal.
“What difference does it make?” retorted McPherson. “Mebbe none tae ye, but he has me pipe in his mouth.”— Paul Anstedt.
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Before marriage a man yearns for a woman; afterwards he just earns for her.
The polls are places where you stand in line for a chance to decide who will spend your money.
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Did you hear about the farmer, who, on his first visit to the big city followed a sprinkling cart for three blocks to tell the driver that the water was all leaking out.
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Three balls in front of a pawnshop mean two to one you won’t get it back.

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