AQUEOUS SOLUTION FOR BLACKENING CHEMICAL CONVERSION TREATMENT OF ZINC OR ZINC ALLOY SURFACE AND METHOD FOR FORMING BLACKENED ANTIRUST COATING FILM USING THE AQUEOUS SOLUTION FOR THE TREATMENT

摘要

Disclosed is a chromium-free surface treatment method which can provide the surface of a metal member having a zinc or zinc alloy surface with good blackness and antirust properties.  Also disclosed is an aqueous solution for chemical conversion which is applicable to the surface treatment method.  The aqueous solution does not contain trivalent or hexavalent chromium ions, but contains, per 1 liter of the aqueous solution, 5-20 g of phosphate ions, 0.1-3 g of divalent iron ions, 1-10 g of divalent manganese ions and 1-3 g of nitrate ions.  The aqueous solution has a pH of 1-3.  A black coating film of Fe3O4 is formed by immersing the metal member in the aqueous solution, then a chemical conversion coating film of cerium oxide is formed thereon, and then a siliceous coating film is formed thereon.