AQUEOUS SOLUTION FOR BLACKENING CHEMICAL CONVERSION COATING OF ZINC OR ZINC ALLOY SURFACE AND METHOD OF FORMING BLACKENED ANTI-CORROSION COATING FILM USING THE AQUEOUS SOLUTION FOR THE CHEMICAL CONVERSION COATING

摘要

The present invention provides a chromium-free surface treating method capable of treating a surface of a metallic member having a surface of zinc or zinc alloy so as to provide good blackness and rust inhibitive performance, and an aqueous solution for chemical conversion coating that can be applied to the treatment method. The aqueous solution contains neither trivalent or hexavalent chromium ion, and contains 5-20 g of phosphate ions per liter, 0.1-3 g of divalent iron ions per liter, 1-10 g of divalent manganese ions per liter, and 1-3 g of nitrate ions per liter. The aqueous solution has a pH of 1-3. A black coating film of Fe3O4 is formed by immersing the metallic member in the aqueous solution, then a conversion coating film of cerium oxide is formed thereon, and then a siliceous coating film is formed thereon.