| 摘要 |
PURPOSE:To form a chromate film having superior corrosion resistance by forming a compd. of a nobler metal on the surface of a galvanized steel sheet and applying a chromating soln. contg. a water-soluble Cr compd., an inorg. sol compd. and a phosphoric acid compd. CONSTITUTION:The surface of a zinc or zinc alloy plated steel sheet is treated with an aq. soln. contg. zinc ions, ions of a nobler metal than zinc such as Fe<2+> or Ni<2+> and oxidizing ions by dipping, spraying or electrolysis to form oxides of zinc and the nobler metal or double oxide of them. A chromating soln. contg. a water soluble Cr compd., an inorg. sol compd. and a phosphoric acid compd. is then applied and dried by heating. The plated steel sheet having a formed chromate film has superior corrosion resistance and is practically used in the naked state. The chromate film exhibits superior performance as an underlayer when the steel sheet is coated.
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