US1904107A - Electroplating with aluminum - Google Patents

Description

April 18, 1933.

vow ZEERLEDER ELECTROPLATING WITH ALUMINIUM Filed Aug. '12. 1930 Malta)? ATTORNEYS.

Patented Apr. 18, 1933.

UNITED STATES PATENT OFFICE mannvon znmnnrm, or' m mmusnn, SWITZERLAND, AssIeNoa-mo 'ntummuu mnusram nxrmnensmscmr, or nnunausmv, SWITZERLAND, A JOINT-STOCK COMPANY OF SWITZERLAND ELECTROPLATING WITH ALUMINUM Application filed August 12, 1980, Serial No. 474,741, and in Germany August 24, 1929.

This invention relates to electroplating with aluminum, and includes both a novel process of coating metals with substantially pure aluminum and the resulting product. The particular utilityof the invention is in the forming of an inte ral aluminum coating upon iron or other errous or base metal, but the invention is applicable to the coating of other metals, including aluminum alloys et cetera.

The main object of the invention is to afford a coated product which combines the properties or advanta es of the-two metals, forexample the mec anical properties or strength of the iron or steel on which the aluminum is deposited as a base, together with the chemical resistance of the substantially pure aluminum coating and its ability to resist corrosion. The commercial utility of the invention covers a very wlde field,

and may be employed for example for any apparatus or mechanical part in which strength or other physical properties are es-- sential, and which it is desirable to protect from rusting or othercorrosion.

Heretofore it has been attempted to coat iron or other base metal with aluminum, one

method having been the rolling and welding of a thin sheet of aluminum upon the base metal object, and another method having been the casting of molten aluminum around the base metal article, or casting the base metal article within a mold previously lined with sheet aluminum. These known methods have never proved satisfactory as the "'coating is not perfect mechanically and is overcoming the objections to the known methods, as Well as to avoid the time and expense incurred in the preliminary manunum upon a base metal, but without practical,

success so far as is known, this being believed to be due to the inability of such methods to deposit an adherent and dense coating, as

is essential, the product having been commercially unavailable due to the formation of deposits of spongy characteror in the form of needles of aluminum; which shortcomings are avoided by the present invention, which affords a coating that is dense and so adherent as not to detach or split.

ofl' even when the coated object, sheet, bar, et cetera is subject to rolling or other working.

Other and futher objects and advantages of the present invention will be explained in; l

the hereinafter following description of an illustrative embodiment thereof, or will be understood to those skilled in the subject. To the attainment of such objects and advantages the present invention consists inthe novel process of electroplating with aluminum, and the novel product thereof, as

well as the novel steps, operations and details, herein illustrated or described.

The present invention may be described in one aspect as consisting in the novel process of electroplating with aluminum which comprises maintaining an electrolytic bath of molten salt, including a salt ofaluminum, and such bath having a melting point lower than that of metallic aluminum, there being immersed in the bath a solid anode of metal containing aluminum, and the object to be coated being the cathode, while passing through the bath from anode to cathode an electrolytic current so as to cause a deposition of substantially pure metallic aluminum upon the object, while the bath is replenished from the metal of the anode. cally the process is one for electrop ating metallic objects composed of iron, or light metal alloys, or other metals with an adherent dense coating of aluminum, and the process being so carried out that not only is aluminum caused to be deposited, but supplementally thereto very small quantities of an much lower. Having thus outlined the generalcharacter of the improved process, the details of a particular embodiment thereof may be'described as follows.

As already indicated the present process is in general an electrolytic deposition from a 'bath composed of suitable molten salt or salts, including a salt or salts of aluminum, the anode being a solid piece of metal containin aluminum, and the cathode being the ob ect, article or piece to be coated which may be a sheet, bar or other shape requiring further working, or a casting or finished mechanical object such as certain parts of engines.

With the present invention density and close adherence are obtained or enhanced by employing a densifying agent and causing it to cooperate in the process. This agent preferably consists of a small quantity of an auxiliary metal caused to be deposited upon the cathode along with the deposit of aluminum. Practical demonstrations have established that in this way the production of spongy or needle-like coatings is avoided and t e deposition is rendered exceedingly dense and adherent. The auxiliary metal is preferably a selected metal, more electronegative than aluminum, and chosen for its cooperative qualities, or there may be small ercentages of more than one other metal. or this purpose lead is found to be advantageous, although othermetals with similar quality are available.

It may be stated that certain ingredients which are invariably present in commercial aluminum, such as iron, carbon and sodium, and very small quantities of which tend to impair seriously the resistance of aluminum to corrosion, can nevertheless be allowed to exist in the anode in the present process, since they will be retained in the anode and selectively excluded in the electrolytic process. For this reason the aluminum coating itself as deposited at the cathode is superior to the metal of the anode in the matter of resistance to corrosion. An anode therefore may be employed consisting eitherof raw aluminum or of aluminum. alloys such for example as are produced by commercial electrothermic reduction.

As an electrolyte having a lower melting point than aluminum, for the purposes of the present invention, there may be employed halogen salts of aluminum mixed with halogen salts of the alkaline metals, or of the alduction or manufacture of highly pure aluminum by aluminum.

The additional or densifying metal of the present invention can be introduced into the process in different Ways. For example it can be added to the electrolyte in the form of a suitable compound or salt of the selected metal or metals. On the other hand special auxiliary or additional anodes may be prepared and maintained in the bath containing the metal or metals to be added. In the case of providing a special separate anode for supplying the additional metal the rate at which the latter passes into the electrolyte and is deposited on the cathode may readily be regulated simply by regulating the tension or electrolytic refining of less pure intensity at such speclal anode of the auxiliary current passed therethrough.

In regard to the quantity or percentage of the auxiliary or densifying metal which is to be added and caused to deposit for the purposes of the present invention, this depends upon the nature of the additional metal, and it can readily be determined once for all by simple tests as to each metal. In the case of lead it is found that a few tenths of one percent are suflicient to give the desired results. In general the smallest practical quantity of auxiliary'metal should be employed that will avoid spongy and needlelike de osits of aluminum, and afford dense and ad erent coatings.

As another factor in perfecting the results of the present process, it is found that the quality of the coating is aided by employing current densities at the cathode as low as ten amperes per square foot, or even less.

The adherence of the coating to the object or cathode will be substantially increased by the following preliminary treatment. Before the commencement of the electro-deposition the circuits may be first reversed so thatthe object to be coated becomes an anode, this being carried on fora short time and operating to prepare and improve the surface to receive subsequently the aluminum deposit.

It is further desirable to clean preliminarily the cathode by brushing or by etching or other treatments known in the art of electroplating.

The resent invention is available for coating wit aluminum in a simple and econom-' process and thereafter submitted to further workin or rolling without causing the splitting o of thecoating. The present process has a special importance. in regard to the coating of various products whose manufacture makes it diflicult or impossible to provide them with a welded coating before they have been given their final definite shape, as for instance, castings extruded sections of li ht metals and the like.

he products of the present invention inelude any objects, such as those referred to,

"t picalf-mod of car h vemel'or'cell 1 contains the molten salt composed of iron or any other" metal and carrying an electroclaeposited coating of substantially ure aluminum, with density of deposit and strength of adherence, and preferably with a very small'percentage'of a metal, more electrone ative than aluminum instrumental in aifor mg thequalities mentioned. M

; The 'accompanying drawing illustrates a jyingout 1 the invention.

' electrolyte or bath 2,in which are immersed one or more'anodes 3 of solid metal contain- 7 ing aluminum. The cathode 4, which may be any metallic object or part,"and is shown as an enginehead casting, is held and suspended in the bath by any sort of holder or clamp 5. Conductors 6 and'7 come from a direct current source, as indicated, and lead respectively to the anodes and cathodes. The bath temperature will bemaintained by external heating means at a point below the meltin points of aluminum and of the electrodes ut above the melting point of the salt mixture constituting the bath.

There have thus been described a novelprocess of electroplatin metals, and the resulting product, em yin the principles and attaining the objects 0 the present invention. Since certain matters of process,

product, step 0 ration and detail'may be variously modi edwithout departing from the principles of the invention it is not intended to limit the inventionto such matters except to the extent set forth in the appended claims.

What is claimed is:

1. The process of electroplatingv metals, such as iron, light metal alloys,etc., with an adherent dense coating of aluminum, wherein the object to be coated is the cathode and the pa e with the aluminum consists wholly of ea v '3. The process as in claim land wherein the density of electrolytic current at the cath-' ,7

ode is maintained not higher than ten amperes per square foot.

4. The process as in claim 1 and wherein short period of time as anode prior to being connected as cathode for the electroplating process for electrolytic action.

5. The process of electroplating with aluminum comprising maintainin an electrolytic bath of molten salt inclu inga salt of aluminum and having a melting point lower than. that of metallic aluminum, with an anode of solid metal containin aluminum and with the object to be coate as cathode the object'to be coated is connected for a therein, and introducing into the process an auxiliary agent containing lead for densifying the deposit.

6. The process of minum com rising maintainin an electrolytic bath 0 molten salts inclu ing a salt ofaluminum and having a melting point lowerthan that of metallic aluminum, with an anode of solid metal containing aluminum and with the object to be coated as cathode thereimand including with the bath or auxiliary anode a small proportion of lead tendelectroplating with aluing to density the deposit without impairing 4 its properties. a

7. The process as in claim 6 and wherein the lead is caused .to be deposited in a proportion of less than one percent of the. total deposit.

8. The process of electroplating aluminum upon a base metal object to afford resistance to corrosion, comprising maintaining an electrolytic bath of molten salt including fa salt of aluminum and having a melting point lower than that of metallic aluminum, with an anode of solid metal containing aluminum and withthe object to be coated as cathode therein, and with a separate anode containing lead as a'densifying metal, not impairing the resistance to corrosion of the product, and passing currents from the anodesto the cathodes, so proportioned that only a very small percentage of the densifying.

metal is incorporated in the deposited coating, to give density and adherence.

III

9. An article of manufacture consisting of' I a metallic base and an electroplated coating thereon comprising substantially pure aluminum of strong adherence and density and such coating containing a very small percentage of lead.

- In testimony whereof, this specification has been duly si ed by.

FRED von ZEERLEDER.

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