Chromating method of zincbased plated steel sheet.

摘要

A chromating liquid for forming a chromate film on a Zn or Zn-alloy plated steel sheet, is prepared by adding and mixing a silane coupling agent in a molar ratio of from 0.05 to 0.3 relative to Cr<6><+> contained in an aqueous chromating liquid which contains 1 - 30g/l of Cr<6><+> and 1 - 30g/l of Cr<3><+> at a weight ratio of Cr<6><+>/Cr<3><+> ranging from 0.1 to 2.0; and further contains 1 - 59g/l of fluoric acid and 1 - 59g/l of phosphoric acid at total of fluoric acid and phosphoric acid ranging from 2 to 60g/l and at a weight ratio of (fluoride ions + phosphate ions)/Cr<3><+> ranging from 0.5 to 3.5. and, further said chromating liquid is applied on a surface of the zinc-based plated steel sheet and is then dried, thereby forming the chromate film having a coating amount of from 10 to 150mg/m<2> in terms of the chromium. <IMAGE>