无铬复合钝化膜的微观组织结构及耐腐蚀性能

目的解决热镀锌钢板表面六价铬钝化工艺所产生的环境污染问题。方法以钼酸铵、纳米硅溶胶、单宁酸、硅烷偶联剂KH151和KH792为主要原料配制新型环保的无铬复合钝化液,在镀锌板表面制备钝化膜。采用扫描电子显微镜(SEM)、能谱仪(EDS)和X射线光电子能谱仪(XPS)分析无铬复合钝化膜表面的微观形貌、元素组成和化学成分,用电化学工作站测试Mo元素对镀锌板耐蚀性的影响,使用中性盐雾实验研究不同皮模量时膜层的耐蚀性。结果无铬复合钝化膜中的Mo元素可以抑制微裂纹的产生和发展,阻挡腐蚀性介质向金属基体扩散,提高复合硅烷膜的电阻。复合钝化膜的电化学交流阻抗比硅烷钝化膜提高了1.6倍,与六价铬钝化膜接近,可以有效抑制腐蚀电化学反应的发生,降低反应速度,提高膜层的耐蚀性。皮膜量为892 mg/m2时,膜层的腐蚀面积为0,耐蚀性达到六价铬钝化膜水平;皮膜量为1252 mg/m2时,耐蚀性能优异。结论制备的无铬复合钝化膜结合了硅烷钝化膜和钼酸盐钝化膜两方面的优点,提高了膜层的致密性和结合性,膜层耐腐蚀性接近/达到了六价铬钝化的效果。

Microstructure and Corrosion Resistance of Chromium-free Composite Passive Film

The work aims to solve the problem of environmental pollution caused by hexavalent chromium passivation process on the surface of hot galvanized steel sheet. A kind of new and environment-friendly chromium-free composite passive solution was prepared, which was mainly made from ammonium molybdate, nano silica sol, tannic acid, silane coupling agent KH151 and KH792. Microscopic morphology, elemental composition and chemical composition of the chromium-free composite passive film were analyzed by SEM, EDS and XPS. The effects of Mo on corrosion resistance of galvanized sheet were tested by electrochemical workstation, and corrosion resistance of the film at different weight was studied by performing neutral salt spray test. Mo element in the chromium-free composite passive film could inhibit generation and development of microcracks, prevent corrosive mediums from spreading toward metallic substrate, and improve resistance of the composite silane film. Electrochemical impedance of the composite passivation film was 1.6 times higher than that of the silane passive film (close to that of Cr6+ passive film), which could inhibit corrosion electrochemical reaction, reduce reaction speed and strengthen corrosion resistance of the film. In addition, corrosion resistance was comparable with that of Cr6+ film as the film reached 892 mg/m2 and corrosion area was 0; and the corrosion resistance was excellent as the film reached 1252 mg/m2. The chromium-free composite passive film combines the advantages of both silane passivation film and molybdate passivation film, compactness and combinability are better, and corrosion resistance of the film is close to/achieves the effect of hexavalent chromium passivation.