磷化/硅酸盐溶胶封闭复合膜的EIS腐蚀机理

Corrosion Mechanism of Phosphated /Silicate Post-Sealed Composite Coatings Based on EIS

采用电化学阻抗谱EIS测量研究了先磷化再硅酸盐溶胶封闭后处理的热镀锌钢在5%NaCl溶液中浸泡不同时间的腐蚀行为,建立了等效电路模型,分析了相关参数的变化规律,探讨了复合膜的腐蚀机理.结果表明:复合膜的耐蚀性随磷化时间的延长而增强,复合膜高电阻、低电容的特性是抑制基底锌层电极反应的关键;随着浸泡时间的延长,镀锌钢的耐蚀性指标变差,腐蚀初期主要发生复合膜的溶解破坏,腐蚀后期主要发生膜层下基体锌层的腐蚀反应.

The corrosion behavior of the phosphated/silicate post-sealed hot-dip galvanized steel in 5% sodium chloride solution was investigated by electrochemical impedance spectroscopy measurement, the equivalent circuit models corresponding to the corrosion processes proposed, the evolution features of the related electrochemical parameters analyzed, and the corrosion mechanism discussed. The results show that the corrosion resistance of the composite coatings increases with an increase in phosphating time. The small capacitance and high resistivity of the composite coatings plays an important role in enhancing the difficulties of the electrode reactions. The corrosion resistance indexes of galvanized steel decrease with the prolonged immersion in 5% NaCl solution. Dissolution and deterioration of the composite coatings occurs at the initial stage of corrosion, while the corrosion reaction of the zinc matrix develops at the later stage.