| 摘要 |
PROBLEM TO BE SOLVED: To provide a surface treatment method of a metal member, by which electrodeposition coatability in a portion of a coating object in a low voltage-applied area can be improved, even when a chemical conversion agent which forms a chemical conversion film having a small number of local low-resistance portions is used. SOLUTION: The surface of a vehicle body W is subjected to a deposition treatment of precipitating Cu on the surface as a preceding step of a chemical conversion film forming treatment, so as to form an uneven state of the surface of the vehicle body W. Then the uneven surface of the vehicle body W is subjected to the chemical conversion film forming treatment, to form a chemical conversion film 21 having a reduced film thickness in a portion (in a concave) between adjoining convexes 40 of Cu than a film thickness in other portions. Thereby, even when a chemical conversion treatment agent which forms a chemical conversion film having a small number of local low-resistance portions is used, the chemical conversion film is formed thinner in a portion between adjoining convexes 40 of Cu on the surface of the vehicle body W, allowing each thin film portion 42 to function as a local low-resistance portion (local conductive portion). COPYRIGHT: (C)2011,JPO&INPIT
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