US1783770A - Process of improving the resistance to corrosion of articles of magnesium and magnesium alloys - Google Patents

Description

l 10 example, the castin latented HQ. 2 1930 UNITED isrATEs mum-- or'rlC-a anoLr are: Ami eus'rav smnanor Bmmnnn, mm, aasrenons To 1 e. rannmrmnus'rnm minnensmracnarr, or rnmnonr-omrrm-m, cum

mm, A conrom'rron or emamr raocass or nrrnovme m nmxs'mncn ro connosron or am: MAGNBBIUI ALLOYS ARTICLES 0! IAGHISIUI Ho Drawing. Application med January :0, ms, Serial no. seam, and in Germany I'ebrnary a, mas,

, Thisvinvention relates to a process of improving the resistance to corrosion f articles I and the like of ma 'nesium and high percenta e magnesium a loys containing] at least 5a out 80% Mg.

Work pieces of high percentage magnesium-alloys frequently contain surface impurities which give rise to an accelerated 'corrosion under certain conditions.- Thus, for

0 skin formed on the-surirequently contains comesium which may give rise to local attack corrosion. Pressed, rolled or otherwise worli'ed up pieces are also superficia-lly covered with a skin in which are emface of cast parts pounds of ma 1 bedded particles of iron and decomposed organic compounds resulting from the use .of

' tools and lubricants, the presence of which,

I particles, even if only in traces, increas es the actionof corroding agents, apparently m consequence of local galvanic action.

Now 'we have ascertained that the resistance of the said alloys against corrosion may be improved .by treating the a boilin (containing about 100 grams .of CrO, per

' liter), for an hour or longer. "B y this treatment anextreinely thin transparent, coating metal pieces wit insoluble in water, containing oxidic chromev compounds and having a yellowish brown hue resembling the color of brass-is deposited on the surface of .themetal; 1': i

' The efiect of the surfaoetreatmentcontemplated by the resent invention-' can-be im- V proved by etching the metal'gpiecesa 'th di-' lute nitric acidlfor example I0% aoi prior. to their treatment with boilin%aqueoujs solutions of dichromates, where y the ?metal pieces are freed from various superficially adhering impurities, such asfor example those arising when the-metal pieces are cast Lthereto.

aqueous solution of dichromates egce tional degree. The modified surface pro need by the dichromate treatment, fur-- v the'rmore, exhibits the advantagepus property of durably retaining lacquer coatings applied ,5

Weclaim: A

1. Theprocess of improving the resistance to corrosion of articles'of magnesium and magnesium alloys containing at least about 8% magnesium, which comprises treating same with a boiling aqueous=solution of di- \chromate's for about-an hour at least. I

2. The process of improving the re'sistance--- to corrosion of articles of mum and magnesium alloys containing at least about 80% magnesium, which comprises trea'ting same witha boiling aqueous solution of dichromates {or about an hour at least; said treatment bein preceded. by a preliminary etching with di lite nitric acid. 3r The process of improving the resistance to corrosion of articles of magnesium and magnesium alloys containing at least about 80% magnesium which comprises treating the same with a boiling solution consisting of a water-soluble dichromate and water, said di-' chromate bein presentin a quantity corres onding to about 109 grams of CrO, per hter, for about one hour at least, Slidftreatment being precededby a preliminary etchiin, sand moulds, and the superficial casting I skin obtained insuch cases is removed;

The herein described pr ss may be ap- 45 plied towork pie'ces pro need by casting,

- 'rolIin ,die-pressing, any other method.-

.provement of the surface qualities, the resistance of these work-pieces to the corrodfiressure-castin on by H) ing eii'ect of aqueous solutions is raised to an y virtue of t is imour hands; I e v f i V ADOLF BECK. v

' GUSTAYiSIEBEL.