GB1417596A - Method of conditioning high aluminium content zinc alloys to receive adherent electroplated metal coatings - Google Patents

Abstract

1417596 Cleaning and conditioning Zn-Al alloys; electro-plating NEW JERSEY ZINC CO 21 June 1973 [14 Sept 19721 29585/73 Headings C7B C7E and C7U A Zn alloy containing substantially 20-22 wt per cent Al is freed of grease and (1) soaked until clean in an aqueous solution containing substantially 2.5 g/l Na 3 PO 4 , 1.5 g/l Na 2 SiO 3 , 0.05 g/l NaOH and 0.5 g/l Na lauryl sulphate, (2) rinsed in an aqueous solution of 3.3-3.5 g/l NaHCO 3 and 1.2-1.3 g/l NaOH, and (3) conditioned in an aqueous solution of substantially 25 g/l NaCN. Degreasing is in halogenated hydrocarbon, e.g. C 2 HCl 3 or C 2 Cl 4 , soaking may be at 140-175‹F for 0.5-2 min at pH 9-11 (adjusted with H 3 PO 4 ), rinsing may be at pH 9-12 for 5-30 sec, at room temperature, and conditioning may be for 1 min. at room temperature. A Cu strike may then be applied by immersing the treated body, with the current switched on, in a bath containing 18.5 g/l Cu cyanide, 30 g/l NaCN, 15.0 g/l Na 2 CO 3 , 22.5 g/l Rochelle salt and NaOH to pH 12 at 131‹F and 40 A/ft<SP>2</SP>; the coating may be 0.00005" thick and a second Cu layer of 0.0003" may be applied before electro-plating with Ni.