| 摘要 |
PURPOSE: To inhibit the diffusion of Mg causing the formation of a brittle intermediate layer and to produce a dense and highly corrosion resistant Zn-Mg alloy plated steel sheet excellent in adhesion by a vapor deposition method. CONSTITUTION: Preliminary Zn vapor deposition is applied to the surface of a steel sheet so that the coating weight of Zn per unit area becomes >=1.5 times the coating weight of Mg, and then, Mg vapor deposition and Zn vapor deposition are applied to the steel sheet held at >=180 deg.C. A starting sheet 1 for plating is surface-activated by reducing heating 12, passed through a reducing atmosphere zone 13, a nitrogen substitution chamber 19, a nitrogen atmosphere duct 20, and a vacuum sealing device 31, and introduced into a vacuum vapor deposition chamber 30. In this vacuum vapor deposition chamber 30, preliminary Zn vapor deposition 40, Mg vapor deposition 50, and Zn vapor deposition 60, 70 are successively clone. At this time, the steel sheet is passed through the nitrogen atmosphere duct 20 under the conditions satisfying X×Z<=1.2 and Y×Z<=35 when X, Y, and Z(sec) represent theO2 , concentration (vol.%) of the nitrogen atmosphere duct 20, H2 O concentration (vol.%), and sheet passing time, respectively. Further, H2 can be added to the nitrogen atmosphere duct 20.
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