| 摘要 |
PROBLEM TO BE SOLVED: To provide a treatment method for forming a black, hexavalent chromium- free chemical conversion coating having corrosion resistance equal to or larger than that of the conventional hexavalent chromium-containing coating on galvanizing and galvannealing. SOLUTION: The treatment solution is used for forming a black, hexavalanet chromium-free coating on galvanizing and galvannealing. In the treatment solution, the molar ratio between nitric ions and tervalent chromium (NO<SP>3-</SP>/Cr<SP>3+</SP>) is <0.5, and the tervalent chromium is present in the form of a water soluble complex with a chelating agent. The treatment solution contains cobalt ions and/or nickel ions, and the cobalt ions and/or nickel ions form a hardly soluble metal salt with the chelating agent, and are stably present in the treatment solution without undergoing precipitation. When galvanizing and galvannealing are brought into contact with the treatment solution, the treatment solution is reacted with zinc, so that a black, hexavalent chromium-free chemical conversion coating containing the zinc, chromium, cobalt and/or nickel, and chelating agent is formed on the galvanizing and galvannealing. COPYRIGHT: (C)2003,JPO
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