| 摘要 |
PROBLEM TO BE SOLVED: To produce a Zn-Al plated steel sheet good in adhesion at a low cost by coating the surface of an Al plated steel sheet with ZnCl2 , thereafter holding the same to the melting temp. of ZnCl2 or above and plating it with Zn. SOLUTION: In a continuous hot-dip Al plating line, Al plating is applied to regulate the coating weight. The surface of the obtd. Al plated steel sheet is coated with ZnCl2 preferably by the coating weight of 15 to 100g/m<2> . After that, this plated steel sheet is held to >=313 deg.C, i.e., the melting temp. of ZnCl2 , preferably, to 313 to 500 deg.C for 0 to 60sec. In this way, the hot-dip ZnCl2 etches the Al plating layer to melt Al oxides on the surface layer and furthermore to activate the surface. Moreover, a substitution reaction of 3ZnCl2 +2Al=3Zn+2 AlCl3 is brought out, This AlCl3 sublimates at about 183 deg.C, and the surface of the Al plating layer is plated with Zn by about >=1μm thickness to impart red rust resistance, chemical convertibility and coating suitability to the Al plated steel sheet.
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