Improvements relating to the production of protective or paint-holding coatings on aluminium or aluminium alloys

摘要

Aluminium or aluminium alloys are treated with an alkaline solution of an alkali metal carbonate and a soluble permanganate which does not react with the carbonate. Preferably, sodium carbonate and potassium permanganate are used and the solution may also comprise sodium chromate, sodium monohydrogen phosphate or other neutral alkali metal salt, chromium carbonate or other carbonate of a metal electro-negative with respect to aluminium, caustic soda or trisodium phosphate. The treatment may be effected by immersion, spraying or brushing. Specification 441,088 is referred to.