US1891549A - Treatment of aluminum alloys - Google Patents

Description

Patented Dec. 20, 1932 UNITED STATES PATENT OFFICE noun 3. LANE, or NIAGARA rALLs, AND WILLIAM 'r. ENNOB, on MAssnNA, NEW

YORK, AssIoNons 'ro ALUMINUM coMrANY or AMnnIcA, orrrr'rsnunon, PENN- sYLvANIA, A conronA'rIoN or PENNSYLVANIA.

TREATMENT OF ALUMINUK ALLOYS No Drawing.

The invention relates to wrought products fabricated from aluminum base alloys and is particularly directed to a method of treating such alloys intermediate the working processes so as to produce a marked improvement in the final product.

The production and use of rivets made from aluminum base alloys has increasedfrom year to year coincident with the increase in production of aircraft. In the field of surface transportation, on railroad vehicles and motor busses, aluminum rivets are in increasing demand where their corrosZon-resistance, lightness, and pleasing natural finish make them desirable. A multitude of other uses might be mentioned.

In supplying this growing demand for aluminum rivets, the manufacturers thereof have encountered difliculties which, although innate and fairl common to the fabrfcation of aluminum shapes and articles by methods involving the plastic deformation of metal, are accentuated by the severe working operations by which aluminum rivets are fabricated. The present invention is directed to the elim nation of these difliculties and, while it will hereinafterbe explained with reference to .the fabrication of aluminum rivets, it is applicable to the fabrication of any aluminum shape or article where difiiculties of a nature like .or similar to those hereinafter described are encountered. r

In commercial processes of making aluminum rivets, the metal is usually cast into ingots which are subsequently elon ated and reduced in diameter by known wor ing processes which form no part of this invention and whose description is unnecessary to those versed in the art. The product obtained by these working processes is, in its final stages, in the shape of large diameter wire which is ultimately cut to "suitable lengths and passed through a rivet making machine wherein the head is formed on the shank, usually by a. single stamping operation, and the article is'ready for use. In this operation, there is a certain amount of wear sufiered -by the rivet forming dies and, although this is looked upon as a necessary evil, means are continually sought for quantities of rivets.

Application filed December 8, 1980. Serial No. 498,847.

reducing this wear and lessening the number of dies required in the production of set In addition to this, the rivet stock in the final stages, and especially in the last head forming operation, is subject to cracking, slivering", bllsterin other defects well known to those famlliar with the operation, as well as the formation of an oxide film consequent to the heating and working processes, which oxide film tends to augmentthe difficulties hereinabove enumerated. Sometimes the cracks are not visibleto the eye until the rivet head forming operation subjects the metal to such a severe strain that the rivet head formed thereon is cracked and must be re'ected. In some. instances,'cracks in the hea or shank of the rivet, quite capable of causing failure in service, are discovered only after the most minute inspection.' It is apparent, therefore, that a distinct advantage would be-obtained by the practically complete elimination of these disadvantages.

We have discovered a treatment which, applied in the stages intermediate the final working processes, is effective in reducingto a substantial extent the number. of rivets cracked, sliveredor otherwise rendered deas a preferred method'an aqueous solution of sodium hydroxide of about 10 per cent or 15 per cent concentration by weight at a temperature close to the boiling point. Consid ering the wide variation in stock diameter necessitated by variation in dimensions of the final rivet, it is-impracticable to specify a set time of immersion but, usin as an index the reduction in diameterof 't e wireby the action of the solution, we have found substantial improvement with a reduction in diameter of only 0.005 inch while if more than usual trouble is being encountered with the particular alloy and product as much 11.9001

inch may be removed. The desideratum is a smooth etched surface without pits and bright and free from oxide film, and simple experiment is sufiicient in determining the beneficial reduction required. A

The coil of wire or other article should be rotatedor otherwise agitated while in the caustic bath to insure even attack by the caustic. After several minutes, more or less, in the immersion bath, the stock is cleansed, by any convenient method, and we have found effective shop practice to consist in a preliminary rinse in water, a momentary dip in a bath of nitric acid of a commercial concentration of about 37 per cent, and a final wash in water after which the stock may be dried either in air or low temperature drying oven. These latter washing and drying details may, of course, be varied to suit commercial convenience, it being only desirable that traces of the caustic which would afl'ect or attack the rivet forming dies be removed.

The caustic immersion is effective if applied either in the later wire drawing stages or the ultimate pause immediately preceding the rivet forming operation. In any case, the improvement produced thereby is quite out of proportion to the few additional handling operations necessary, and we have found that by the use of 'our invention, rivets may be produced rapidly and efiiciently with considerably less rejections 0r failures as a result of the forming operations, and with less wear on the dies.

The process has also been found applicable to certain difiicult fabrication operations both inethe final rolling of sheet and other wrought products in the manufacture of which plastic deformation of the metal occurs. Unsightly blisters and surface defects of a more serious nature are prevented in their inception by a caustic dip in intermediate forming processes substantially as above described. In all manner of forming and working operations which involve the plastic deformation of metal, advantages will accrue from use of the methods of our invention.

It is to be distinctly understood that wherever in this specification or in the claims appended hereto the term aluminum or aluminum alloy or aluminum base alloy 001 curs, it includes any alloy of aluminum containing morethan about 50 per cent aluminum. It is also to be understood that the term caustic solution, while herein usually described as consisting of a sodium hydroxide solution, is intended to include solutions of similar characteristics such as potassium hydroxide, etc., the proper concentrations of which can easily be determined, this factor being significant to the extent thatit affects the time of immersion in the caustic bath.

1. A method of producing an improved wrought article formed from an aluminum base alloy which comprises plastically deforming the metal of said alloy by a series of metal working operations and immersing the partially formed article in a caustic solution prior to the final metal working operation. a

2. A method of fabricating an aluminum alloy rivet characterized by substantial freedom from surface defects incident to working, which comprises plastically deforming the metal of said aluminum alloy from which said rivet is fabricated, said plastic deformation being effected by a plurality of metal working operations, and immersing the partially formed rivet in a caustic solution prior to the final'metal working operation.

NORMAN B. LANE. WILLIAM T. EN N OR.

Having thus described our invention, we

claim