稀土元素对镀锌层三价铬彩色钝化膜耐蚀性的影响

为了提高三价铬彩色钝化膜的耐蚀性,在三价铬钝化液中加入稀土元素(La3+,Ce3+,Ce4+),通过乙酸铅点滴试验、Tafel曲线和盐水浸泡试验研究了稀土元素含量对镀锌层彩色钝化膜耐蚀性的影响。结果表明,加入稀土元素后,不用进行封闭处理也能提高钝化膜的耐蚀性,其中Ce4+的作用最显著,当钝化液中Ce(SO4)2.4H2O浓度为5.0 g/L时:钝化膜乙酸铅点滴耐蚀时间由镀锌层的19.33 s提高到157.56 s;腐蚀电位由-1.006 V正移至-0.982 V,腐蚀电流密度由3.268×10-5A/cm2减小到1.116×10-5A/cm2;耐盐水腐蚀能力提高,浸泡336 h仍未出现锈点,失重缓慢;钝化膜呈均匀的黄绿色,表面形成了均匀、平滑、较深的构槽,有利于提高膜层的耐蚀性。

Effect of Rare Earth on Corrosion Resistance of Trivalent Chromium Color Passivation Film on Electroplated Zinc Coating

Rare earth elements(La3+,Ce3+ and Ce4+) were introduced into trivalent chromium passivation fluid.The effect of rare earth content on the corrosion resistance of the color passivation film on electroplated Ni coating was investigated by dripping test of aqueous lead acetate,measurement of Tafel curves,and saline water soaking test.It was found that the addition of rare earth contributed to improved corrosion resistance of trivalent Cr passivation film even in the absence of sealing,and Ce4+ was the most effective in improving the corrosion resistance.When Ce(SO4) 2.4H2O was introduced into the passivation fluid at a concentration of 5.0 g/L,the endurance of the trivalent Cr passivation film against dripping of lead acetate was increased from 19.33 s to 157.56 s,while its corrosion potential was shifted from-1.006 V to-0.982 V and its corrosion current density was reduced from 3.268×10-5A/cm 2 to 1.116×10-5 A/cm 2.In the meantime,introducing 5.0g/L Ce(SO 4) 2.4H 2 O helped to improve the resistance of trivalent Cr passivation film against saline water.After being immersed in saline water for 336 h,the film was still free of rusted locations and lost weight slightly.Moreover,the surface of the greenish yellow passivation film had even and deep grooves,which were in favor of improving the corrosion resistance of the passivation film.