| 摘要 |
PROBLEM TO BE SOLVED: To obtain a coating film having excellent corrosion resistance almost without changing the brightness and the color tone of a bare surface by dipping magnesium or a magnesium alloy in an electrolyte containing a phosphate and an aluminate and treating the surface with anodic oxidation. SOLUTION: The concentration of the phosphate is preferably 0.05-0.2 M and the concentration of the aluminate is preferably 0.2-1 M. The electrolyte prepared by adding an organic compound bath stabilizer having a hydroxyl group in addition to the phosphate and the aluminate is suitable and as the bath stabilizer, glycerine, ethylene glycol or the like is used and the concentration is controlled to 1-20 g/l and 10-50 wt.% stabilizer based on the weight of the aluminate is suitably used. After the anodic oxidation, the coating film is sealing treated by dipping it in hot water. The hot water is a pure water of >=85 deg.C and the treating time is preferably 3-15 min. The anodic oxidation coating film is controlled to have a thickness, in which the brightness and the color tone of the metallic base is not changed, and preferably to <=0.1μm.
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