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Melanization is harmful to the lightness of galvanized steel surface and also reduces the bonding force between a paint coat and the steel sheet. Experimental results showed that the hypothesis of Zn-Pb codeposition does not hold true, while the fact that PbSO4 micelles in sulfate bath settle on the coating surface support the second hypothesis. The authors come to the conclusions that (1) Any measure to eliminate PbSO4 micelles before or after passivation of the coating will prevent melanization; (2) PbSO4 micelles adsorbed on the surface of passivated film promote the growth of oxygen-deficient Zn oxide and result in the generation of melanization.
Melanization is harmful to the lightness of galvanized steel surface and also reduces the bonding force between a coating and the steel sheet. Experimental results showed that the hypothesis of Zn-Pb codeposition does not hold true, while the fact that PbSO4 micelles in sulfate bath The authors come to the conclusion that (1) Any measure to eliminate PbSO4 micelles before or after passivation of the coating will prevent melanization; (2) PbSO4 micelles adsorbed on the surface of passivated film promote the growth of oxygen-deficient Zn oxide and result in the generation of melanization.