AZ91D镁合金有机复合涂层的腐蚀防护性能

AZ91D镁合金易腐蚀,单项处理防腐蚀效果不大。先分别对其作无铬转化和微弧氧化预处理,再阴极电泳底层,最后喷涂面漆,获得了无铬转化层/阴极电泳层/有机涂层和微弧氧化层/阴极电泳层/有机涂层。采用附着力及铅笔硬度测试、盐雾试验、电化学试验对2种有机复合涂层的形貌、多种性、防腐蚀效果及其机理进行了探讨。结果表明:2种有机复合涂层都能显著提高AZ91D镁合金的耐腐蚀性能,使其自腐蚀电位分别约提高130 mV和80 mV,腐蚀电流密度约降低40%和70%,极化电阻约提高4倍和7倍;2种涂层的附着力达到1级以上,铅笔硬度达到7 H以上;微弧氧化预处理后获得的有机复合涂层的腐蚀防护效果比无铬转化预处理的好。

Corrosion-Prevention Performance of Organic Composite Coatings on AZ91D Magnesium Alloy Substrate

AZ91D Mg alloy substrate was pretreated by Cr-free conversion or micro-arc oxidation (MAO), followed by cathode electrophoresis generating the primer layer and spraying generating the top coating. These processes gave rise to two kinds of composite coatings (Cr-free conversion coating/electrophoresis coating/organic coating and MAO coating/electrophoresis coating/organic coating). The performance of the two kinds of composite coatings was evaluated using adhesion test, pencil hardness test, salt-spray test and electrochemical test, and their anti-corrosion mechanisms were discussed. It was found that the two kinds of composite coatings could both significantly improve the corrosion resistance of the Mg alloy. Namely, they could increase the corrosion potential of the Mg alloy by about 130 mV and 80 mV, reduce the corrosion current density by about 40% and 70%, and increase the polarization resistance by about 4 times and 7 times. In the meantime, both composite coatings possessed adhesion force of over grade 1 and hardness of over 7 H. The composite coating pretreated by MAO possessed better corrosion-prevention performance than the other one.