| 摘要 |
PURPOSE:To improve the corrosion resistance, weldability and workability of a steel sheet for an automobile by successively plating at least one side of the steel sheet with a Zn-Co alloy having a specified composition and a Zn-Co alloy contg. a reduced amount of Co by a specified extent of deposition each. CONSTITUTION:The 1st layer of a Zn-Co alloy contg. 6-30wt% Co and 0.01- 3% Cr, alumina, silica, titania or the like and having 1-10g/m<2> extent of deposition and the 2nd layer of a Zn-Co alloy contg. 0.1-6% Co and 0.01-3% Cr, alumina, silica, titania or the like and having 3-30g/m<2> extent of deposition are successively formed on at least one side of a steel sheet by plating to obtain a surface treated steel sheet having high corrosion resistance. This double-plated steel sheet can easily endure internal and external corrosive environments by changing the thicknesses of the alloy layers.
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