磷化/钼酸盐后处理的热镀锌钢板的电化学行为

Electrochemical Behaviors of Phosphated/Molybdate Post-Sealed Hot-Dipped Galvanized Steel Sheet

将热镀锌钢板先磷化再用钼酸盐溶液进行封闭后处理,通过塔菲尔极化和电化学阻抗测量研究其在5%NaCl水溶液中的腐蚀电化学行为,并与单磷化的热镀锌钢板进行了对比.结果表明:磷化的热镀锌钢板再经钼酸盐封闭处理后,阳极极化和阴极极化均明显增强,腐蚀保护效率显著提高,发挥了单磷化膜和单钼酸盐膜耐蚀性能的协同效应,电化学阻抗值提高了一个数量级以上;在5%NaCl水溶液中浸泡的初期,低频扩散阻抗值随浸泡时间延长而增大,表明复合膜具有一定的自修复能力.

The hot-dipped galvanized （HDG） steel sheet was phosphated and then post-sealed using molybdate solution. Also, the corrosion performances and electrochemical behaviors of the phosphated/molybdate post-sealed HDG steel sheet in 5% NaCl solution were investigated, using Tafel polarization and electrochemical impedance spectroscopy （EIS） measurements. The results were finally compared with those of the steel sheet only with phosphating process. It is found that, after the post-sealing of the phosphated HDG samples With molybdate solution, the anodic and cathodic processes of the zinc corrosion are conspicuously suppressed, the corrosion protection efficiency markedly increases, and the electrochemical impedance increases by more than one order of magnitude. All this reveals a synergistic effect of the corrosion resistances of the phosphate coatings and the molybdate films. It is also found that the low-frequency diffusion impedance increases with the immersion time at the initial stage of immersion in 5% NaCl solution, which demonstrates clearly the self-repairing capability of the composite coatings.