热浸镀锌层上钼酸盐转化膜的腐蚀电化学性能

    将热镀锌钢在含10 g/L Na₂MoO₄·2H₂O、pH为5的溶液中60℃下处理10~300秒,获得了钼酸盐转化膜试样.应用极化曲线和电化学交流阻抗谱(EIS)研究了转化膜层在5% NaCl水溶液的耐蚀性能.结果表明,经钼酸盐转化处理后的镀锌钢板,其腐蚀电流密度下降,极化电阻升高,阴极极化作用明显增强,腐蚀保护效率显著提高,电化学阻抗值提高了一个数量级;低频扩散阻抗值随处理时间的增加先增大后减小,表明腐蚀电解质在转化膜层孔隙中扩散的难易程度先增加后下降.

ELECTROCHEMICAL BEHAVIOUR OF MOLYBDATE CONVERSION FILM ON HOT-DIP GALVANIZED STEEL

    Hot-dip galvanized(HDG)steel sheets were treated for 10~300 s by a molybdate aqueous solution containing 10 g/L Na₂MoO₄·2H₂O(pH=5,60℃).The corrosion electrochemical behavior of the molybdate conversion films was compared to that of bare samples in 5% NaCl solution using polarization curves and electrochemical impedance spectra(EIS).The results show that the corrosion current density decreases and the polarization resistance increases of the HDG after molybdate conversion treatment.While the molybdate conversion films can conspicuously suppress the cathodic processes of the zinc corrosion,thereby its corrosion resistance remarkably increases as well as the electrochemical impedance increase by about one order of magnitude.It is also found that the low-requency diffusion impedance initially increases and then decreases with the increasing treatment time,which demonstrates clearly that the resistance to the migration of electrolyte through the conversion films initially increases and subsequently decreases with the increasing of the treatment time.