| 摘要 |
PROBLEM TO BE SOLVED: To improve the corrosion resistance, lubricity and weldability, on the surface of a galvanized steel sheet, by forming a zinc phosphate film layer essentially consisting of zinc phosphate and a phosphate film layer essentially consisting of a phosphate essentially composed of one or more kinds of metals among Mg, Al, Co, Mn and Ca thereon. SOLUTION: The zinc phosphate film layer improves, by anchor effect, its adhesion for a coating material, prevents the direct contact of the steel sheet and a tool at the time of sliding and contributes also to the improvement of its lubricity. The phosphate film layer improves its corrosion resistance. The phosphate film preferably contains the phosphate of Mg and/or Al as the main components in particular, the molar ratio of Mg/P is controlled to 0.4/2 to 1/2, and the molar ratio of Al/P is controlled to 0.3/3 to 1/3. The total film coating weight including the zinc phosphate film and the phosphate film is suitably controlled to 0.5 to 4 g/m2 per side of the steel sheet. Moreover, the ratio of the coating weight of both films is suitably controlled to the phosphate film/zinc phosphate film =1/100 to 100/100.
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