METHOD FOR OBTAINING ALUMINUM AND/OR MAGNESIUM EXCELLENT IN CORROSION RESISTANCE BY REMOVING OXIDE FILM WITHOUT USING CHROMIUM COMPOUND

摘要

PROBLEM TO BE SOLVED: To form a base surface for forming a chromate coated film on the surface of aluminum or magnesium by using a treating solution not containing hexavalent chromium or ferricyanide. SOLUTION: The surface of metal is brought into contact with a solution for desmutting/removing an oxide film and then rinsed with rinse containing at least one chelating agent. As the solution for desmutting/removing the oxide film, a strong acid solution containing, as indispensable components, nitric acid and Fe3+ ion and further containing one kind or more selected from anions including molybdic acid ion, persulfuric acid ion and fluorine, sulfuric acid and a surfactant is used. The chelating agent can be selected from gluconic acid, tartaric acid, ethylenediaminetetraacetic acid, EDTA and NTA.