GB626693A - Improvements in and relating to the surface treatment of aluminium and aluminium base alloys - Google Patents

Abstract

626,693. Electroplating on aluminium &c. WATSON, H. R., and WARD, A. T. Oct. 23, 1945, No. 27903. [Class 41] Aluminium or aluminium base alloys are treated prior to being plated with another metal by immersion in a solution containing a sodium compound, a nickel compound, a tin compound, a carbonate, a chloride and a hydroxide, the tin being present in amounts not less than would be provided by “ oz. stannous chloride in 1 gallon water, the nickel and carbonate being present in amounts not less than would be provided by “ oz. of nickel carbonate in 1 gallon water, and the hydroxide being present in amounts not less than would be provided by 3 ozs. caustic soda in 1 gallon water. The solution may contain alcohol and ether, have a pH value not less than 8, and be maintained at a temperature of 150‹ to 180‹ F. In an example, 4 ozs. sodium stannate and 1.5 ozs. nickel chloride are dissolved in 1 gallon water, and to the solution are slowly added 12 ozs. sodium hydroxide and 1 oz. sodium carbonate. The article to be treated is immersed in the solution maintained at the above temperature, for 30 to 40 seconds, and may be made the anode or the cathode respectively to remove hydrogen or oxides from the surface. It is then rinsed in cold water, cleared in a nitric acid dip, again rinsed, and finally transferred to a copper, brass, zinc or tin primary plating bath, examples of which are given below, where it is " struck for 30 to 40 seconds, and then plated at normal current density for 10 to 15 minutes. It may then be given a final coating in a further plating bath of the same or another metai such as nickel, chromium, silver, gold or rhodium. In a second example the treating solution comprised 4 oz. stannous chloride, 1 oz. each of nickel carbonate and sodium carbonately and 14 oz. caustic soda, in 1 gallon water. The copper primary bath may comprise 10 grams sodium carbonate, 20 grams sodium bisulphite, 30 grams potassium-copper cyanide, 1 gram potassium cyanide, and 2 grams potassium hydroxide, in 1 litre water. The brass primary bath may have 37 grams cupro-cupric sulphitezinc sulphite (Cu 2 SO 3 CuSO 3 ZnSO 3 .3H 2 O), 44 grams potassium cyanide, 2 grams ammonium chloride, and 10 grams potassium hydroxide in 1 litre water, with brass anodes, and -may work at 85‹ F. Zinc primary bath : 30 grams sodium zinc cyanide, 7 grams sodium cyanide, ¢ gram sodium hyposulphite, 14 grams sodium hydroxide, and 6 ccs. polyvinyl alcohol, in 1 litre water. Tin primary bath : 20 grams sodium stannate, 18 grams sodium hydroxide, 10 grams sodium acetate, and 0.75 gram sodium percarbonate, in 1 litre water, used at 130‹ F.