ACIDIC AQUEOUS SOLUTION AND METHOD FOR PASSIVATING SURFACE OF ZINC OR ZINC/ALUMINUM ALLOY

摘要

An aqueous acidic treating solution for forming a chromium-containing passivate coating on the surface of zinc or zinc-aluminium alloys contains chromium ions of which the predominant proportion are in the hexavalent state, preferably in an amount 2-20 g/l., nitrate ions, preferably in an amount 0.5-6 g/l., and phosphate ions, preferably in an amount 1-15 g/l. The solution may also contain fluoride ions, molybdate ions and tungstate ions. The phosphide may be an alkali metal or ammonium phosphate, a polyphosphate or phosphoric acid.