Swiss Aluminium Ltd.

Jean Francois Paulet

Bruno Boetsch

The object of this invention was to find a Sn.sup.II -containing electrolyte for galvanizing or coloring anodized aluminum and its alloys which, in the first place, contains substances which stabilize Sn.sup.II better than substances used up to now for this purpose, secondly, exhibits better throwing power and therefore better current distribution and thirdly is not harmful to the environment, or at least not to such a degree as the electrolytes used up to now. The electrolyte of the invention is such that it contains one or more additives having the general structure R.sub.1 --S--R.sub.2, where R.sub.1 can be a hydrogen atom or a hydrocarbon group with or without a hydroxy or carboxy group, R.sub.2 a hydrocarbon with hydroxy or carboxy group. A particularly preferred additive is 2.2'-di-hydroxy-di-ethyl-thio-ether (or 2.2'-thio-di-ethanol) HOCH.sub.2 CH.sub.2 --S--CH.sub.2 CH.sub.2 OH.

Acidic electrolyte containing Sn.sup.II ions

The invention allows one to obtain a strongly adherent dark grey to black coating, with good corrosion resistance, on aluminium and its alloys. The degreased aluminum is pre-treated in an aqueous solution containing at least one salt of a metal which is less electronegative than aluminium. It is then colored in another aqueous solution containing molybdate ions and at least one fluorine compound and/or a heavy metal chloride, and/or an organic chlorine compound with active chlorine atoms.

Growing community of inventors

Siblingen, Switzerland

Jean Francois Paulet