GB1277523A - Tin-coated aluminium - Google Patents

Abstract

1277523 Tin alloy coatings; removing oxides electrolytically FURUKAWA ELECTRIC CO Ltd 15 April 1970 [15th April 1969 (2) 23 April 1969 (3) 21 May 1969 25 Dec 1969] 17880/70 Headings C7B and C7F In a process for the preparation of a tin alloy coating on the surface of an Al or Al alloy article, the surface of the article is first contacted with a molten inorganic halide salt bath at a temperature below the melting-point of aluminium, to remove oxide, either (a) by anodic treatment of the Al while in contact with a molten salt bath in which the bath comprises any one or more of a halide of a heavy metal, other than a stannous halide, an aluminium halide, an alkali metal halide, an alkaline earth metal halide and a stannous halide/ aluminium halide mixture or (b) by "chemical" treatment of the Al with a molten salt bath comprising a stannous halide/Al halide mixture, and the thus treated surface is contacted with a molten Sn or Sn alloy bath each of which contains 0.5-30 wt per cent Sb. Prior to oxide removal, the Al may be Zn flash-coated by the conventional zincate treatment. Anodic treatment may be a fused bath containing halides of Fe, Co, Ni, Zn, Zr, stannic Sn, Sb, Pb, Bi, Cd, Ti, Na, K, Mg, Ca, Sr or Ba, chlorides being preferred and a current of 0.5-20 A/dm<SP>2</SP> for 300-15 secs. being used; chemical removal of oxide may be effected in a stannous halide (e.g. SnCl 2 )/Al halide mixture which also comprises Na, K, or Li halide, or a zinc salt so that a chemical Sn/Zn conversion coating is formed on the Al simultaneously with oxide removal. A hot-dip coating is then applied in a Sn or Sn alloy bath containing 0.5-30 wt per cent Sb, and, optionally Cd, Zn, or Bi. A strip or wire may be coated continuously, a wiping device removing excess metal.