The process of rare earth lanthanum conversion coating for galvanized steel was studied by orthogonal experiment The optimized passivation parameters were obtained as follows, the concentration of La(NO3) 30 g/L, H2O2 20 ml/L, pH 4 and passivation at 40 °C for 30 s. The corrosion resistance was examined by weight loss test, neutral salt spray test and electrochemical impedance spectruscopy. The results showed that the corrosion impedance of the pretreated sample was significantly improved, the corrosion rate was decreased by one order of magnitude, and the anti-white rust time was 54 h. Scanning electron microscopy (SEM) showed that the conversion coat covered the surface of zinc compactly.%通过正交试验确定了稀土镧盐钝化镀锌钢板的最佳工艺条件为:30 g/L硝酸镧、20ml/L双氧水、pH值为4、40℃下钝化30 s.利用碱浸失重试验、中性盐雾试验和电化学阻抗谱评价了钝化膜的耐腐蚀性能.结果表明,经稀土镧盐处理后的试样阻抗值相对于空白试样大幅度提高,腐蚀速率降低1个数量级,抗白锈时间达54 h.扫描电镜(SEM)结果表明,稀土镧盐钝化膜对基体的覆盖度较高.
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