化学镀镍磷层氯酸盐钝化膜的耐蚀性能及耐蚀机理

铬酸盐钝化可以提高薄的化学镀镍层的耐蚀性,防止镀层在空气中变色。为消除铬对环境的影响,开发了无铬钝化工艺。常温下,将化学镀镍磷试样浸入无铬钝化液中浸泡3 min,在镀层表面制备了无色钝化膜。通过孔隙率测试、盐雾试验、极化曲线、扫描电镜及XPS能谱分析,对钝化膜的耐蚀性和成膜机理进行了研究。结果表明:镀层经钝化后耐变色性能获得极大提高,孔隙率由45个/dm2降低到3个/dm2;自腐蚀电位从-407 m V正移至-303 m V;自腐蚀电流密度降低了1个数量级以上;中性盐雾试验暴露100 h后保护评级由5级提高至10级。由此可见:钝化膜显著降低了化学镍磷镀层的孔隙率,并大大提高了化学镀镍层的耐蚀性。最后通过XPS发现,钝化膜主要物相组成为Ni O和Ni(OH)2。

Corrosion Resistance and the Mechanism of Chlorate Passivation Film on Electroless Ni-P Coating

Chromate passivation can improve the corrosion resistance of thin electroless nickel coating and prevent the coating from discoloring in the air. In order to eliminate the influence of chromium on the environment,a chromium-free passivation process was developed. A colorless passivation film was prepared on the surface of electroless Ni-P coating by immersing it in chromium-free passivation solution for 3 min at room temperature. The corrosion resistance and formation mechanism of passive film were studied by porosity test,salt spray test,polarization curve,scanning electron microscope and XPS energy spectrum analysis. Results showed that the anti-discoloration performance of the passivation coating was greatly improved,and the porosity amount was reduced from 45 per dm2 to 3 per dm2. Furthermore,the self-corrosion potential shifted from-407 m V to-303 m V,and the self-corrosion current density decreased by more than one order of magnitude. The protection rating was improved from 5 to 10 after 100 h exposure of neutral salt spray test. Thus,the passivation film could reduce significantly the porosity of the passivation coating and enhance the corrosion resistance. Finally,XPS analysis displayed that the main components of passivation film were Ni O and Ni( OH)2.