| 摘要 |
PURPOSE:To form a dense and beautiful protective film which has excellent wear resistance, workability and corrosion resistance and does not ruin the appearance by subjecting a galvanized steel sheet to a blackening treatment then forming single or plural layers of coating type chromate films on the surface thereof. CONSTITUTION:Single or >=2 layers of the plating layers of a Zn alloy which consists essentially of Zn and contains >=1 kinds of Ni, Co or Mo at 0.5-30wt% Ni and Co and 0.5-10% Mo. Such galvanized steel sheet is subjected to the blackening treatment by a blackening treating liquid contg. 0.1-20% acid such as hydrochloric acid and 0.1-20% oxidizing agent such as hydrogen peroxide water. Single or >=2 layers of the coating type chromate films are formed on the surface of the steel sheet after the above-mentioned treatment or the above- mentioned chromate films and/or single or >=2 layers of the films are formed by coating a soln. contg. >=1 kinds among silicic acid colloid, water glass, silane coupling agent, org. resin, aq. resin, and chromic anhydride on the surface and drying the coating. The protective film for the black galvanized steel sheet is thereby formed.
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