GB722449A - Cadmium plated aluminum and the method of making the same - Google Patents

Abstract

722,449. Coating aluminium articles. BENDIX AVIATION CORPORATION. May 1, 1952 [May 4, 1951], No. 11047/52. Class 41. [Also in Group II] A body of, or containing, aluminium is coated successively with zinc, copper or nickel, cadmium and a chromate, and the article is then baked. The preferred sequence of operations is shown in the flow sheet. The emulsion cleaner employed in stage 2 may be a hydrocarbon solvent, a soap, preferably watersoluble, made with caustic potash or caustic soda and fats or oils or sulphonated oils, a solvent or diluent such as pine oil, cresylic acid or lower aliphatic alcohols and a little water. The alkali cleaner, stage 4, may consist of a solution of alkali metal carbonates, silicates, phosphates or borates or may be a sodium hydroxide solution buffered with tri-sodium phosphate or sodium silicates, preferably orthosilicate at 160-200‹ F. The acid dip, stage 6, consists of nitric acid or a mixture of nitric and hydrofluoric acids at room temperature according to the nature of the work treated. The zinc plating, stage 8, is effected by simple immersion in a basic sodium zincate solution of 40-42‹ BÚ at temperature 50-90‹ F. The nickel or copper plating stage 10 is effected electro lytically. A nickel bath may consist of an aqueous solution of 16 oz. nickel sulphate, 3 oz. ammonium chloride and 4 oz. boric acid per U.S.A. gallon. The plating current should be applied as soon as the article has entered the bath. A suitable copper bath contains 3.5- 4.5 oz. copper cyanide, 0.75-1.5 oz. free cyanide per U.S.A. gallon with addition of 6-8 per cent of an oily solution of potassium-sodium tartrate. Cadmium plating, stage 12, is effected electrolytically from a bath made up of 3 oz. cadmium oxide, 1 oz. sodium hydroxide and 12 oz. sodium cyanide per U.S.A. gallon of water; the bath may contain up to 9, preferably 3-5 oz. per sodium carbonate per U.S.A. gallon. For barrel plating the quantities of cadmium oxide and sodium cyanide are increased to 6 oz. and 24 oz. respectively. The article should be introduced wet into the bath and the plating current simultaneously applied. The immersion bath employed in stage 14 consists of chromic acid with relatively minor amounts of sulphuric and acetic acids. The bath employed in stage 16 may consist of a solution of 2 oz. sodium hydroxide per U.S.A. gallon. Baking, stage 18, may be at 250 F. Detailed examples are given for the treatment of (a) a die-cast connector shell containing 10 per cent silicon, 85 per cent aluminium and the balance various other metals, (b) a wrought bar of pure aluminium.