添加Co(Ⅱ)和硅溶胶的热镀锌铝合金层三价铬钝化膜的抗腐蚀性能

Effect of Introducing Cobalt Salt and Silica Sol on Corrosion Resistance of Trivalent Chromium Passivation Coatings on Hot-Dip Galvanized Zinc-Aluminum Steel

为进一步提高热镀锌铝钢三价铬钝化膜的耐蚀性,分别或同时向三价铬钝化液中加入Co(Ⅱ)、硅溶胶进行钝化,通过中性盐雾试验、极化曲线测试及形貌观察、成分分析,考察了硅溶胶、Co(Ⅱ)盐对三价铬磷酸盐钝化膜耐蚀性的影响,考察两者的协同效应。结果表明:硅溶胶和Co(Ⅱ)盐的加入均能有效提高三价铬钝化膜的耐蚀性,两者同时添加时转化膜耐蚀性更好;硅溶胶的加入对钝化膜起到了很好的填充作用,少量Co(Ⅱ)盐使膜层表面晶格歪曲,抑制活性点的过度生长,可防止尖刺生成;同时添加Co(Ⅱ)和硅溶胶的三价铬钝化液所得的钝化膜中磷酸锌、磷酸铝生成时伴随磷酸铬和磷酸钴生成,二氧化硅在最外层,后期填充形成外表层,表层同时有一定量的磷酸锌。

Co(Ⅱ) salt and silica sol were separately or jointly introduced into trivalent chromium passivation fluid to improve the corrosion resistance of trivalent chromium conversion coating on hot- dip Zn- Al alloy.The effect of the Co(Ⅱ) salt and silica sol on the corrosion resistance of the trivalent chromium passivation coating was investigated with neutral salt spray test,polarization curve measurement,morphology observation and composition analysis,and the synergistic effect between Co(Ⅱ) salt and silica sol was discussed.Results showed that the addition of the silica sol and Co(Ⅱ) salt in the trivalent Cr passivation fluid helped to effectively improve the corrosion resistance of the trivalent chromium conversion coating,and Co(Ⅱ) salt and silica sol exhibited synergistic anticorrosion ability.The silica sol added in the passivation fluid was able to well fill the pores of the passivation coating;on the other hand,a small amount of Co(Ⅱ) in the passivation fluid was able to distort the crystal of the passivation coating,restrain excessive growth of active points and retard the formation of spiky structure.When Co(Ⅱ) salt and silica sol were simultaneously added into the trivalent passivation fluid,as-obtained passivation coating mainly consisted of zinc phosphate and aluminum phosphate as well as accompanied chromium phosphate and cobalt phosphate.Besides,silica was present mainly on the surface of the passivation coating and was ready to fill the pores therein,while there was also a certain amount of zinc phosphate on the coating surface.