| 摘要 |
PROBLEM TO BE SOLVED: To allow the plated article to exhibit excellent corrosion resistance in a strong corrosive environment by applying the outside of a 1st hot dip galvanizing layer with hot dip galvanizing as a 2nd layer with a zinc bath obtd. by simultaneously adding specified amouts of Mg, Ni or Si to a zinc bath contg. a specified amt. of Al. SOLUTION: The amt. of Al in a zinc bath in a 2nd layer plating stage is controlled to about 2 to 20%, and, moreover, 0.01 to 5% Mg and 0.01 to 5% Ni or Si are simultaneously added. Mg is added for the purpose of clearly separating an Al-Zn structure high in the contents ofβ-Zn and Al and granulating this structure. Then, Mg stays in the structure and improves the granular corrosion resistance of Al and Zn in the structure to extremely reduce the amt. of corrosion loss and to suppress the progression of corrosion as well. Moreover, Ni or Si stays in a plating columnar layer to suppress the development of an Fe-Zn-Al alloy layer. The blending ratio of Mg to Ni or Si is preferably controlled to 1:1.
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