Abstract: A process for the production of white and black oxide ceramic surface films on silicon-containing light metal cast alloys by plasma-chemical anodic oxidation. An aluminum cast alloy is pickled with nitric acid and hydrofluoric acid and coated by plasma-chemical anodic oxidation in an aqueous electrolyte. Accordingly, a coating variant is provided particularly for construction parts of silicon-containing light metal cast alloys having complicated shapes which enables the production of uniformly thin oxide ceramic surface films in contrast to conventional coating variants.

Abstract: By means of an electrolyte free of ammonia, cyanide, and fluoride, hence low in harmful substances and inoffensive to the environment, optically black coatings having a thickness of less than 10 microns and substantially equal optical absorption and thermal emission capability can be produced on light metals or alloys thereof by spark discharge anodizing. In comparison with prior art conversion coatings obtained by spark discharge anodizing, the coatings produced with this electrolyte have a substantially lower roughness of this electrolyte in spark discharge anodizing provides an alternative mode of coating particularly for structural components or subassemblies of complicated shapes having greater requirements for accuracy to gauge.