不同电压下钼酸钠对镁合金微弧氧化膜的影响

摘要

By means of adding natrium molybdate into silicate system(electrolyte),the influence of natrium molybdate on corrosion-resistance of micro-arc oxidation coating on AZ91D magnesium alloys was investigated comparatively under different applied voltages.The thickness,surface morphologies,and phase composition of the coating were tested with TT260 digital coating thickness gauge,SEM,and XRD,respectively.Corrosion resistance of coating was evaluated by means of drop test and electrochemical test.The result showed that,after adding Na2MoO4 into the electrolyte,the coating thickness would change slightly,the coating corrosion resistance determined by drop test would reduce somewhat,and the corrosion resistance determined by electrochemical test would exhibit increasing trend,instead.And the coating anticorrosive performance would be the best when adding 0.42 g/L Na2MoO4 under high voltage,being higher by one order of magnitude than that under low voltage,31 times higher than that without additives,and was approximately two orders of magnitude higher than that of the substrate.Meanwhile,a browncolored coating could be obtained on the surface of AZ9lD magnesium alloy owing to the formation of MoO2,which would be soluble slightly in HNO3,but stable chemically in NaCl medium used for electrochemical test,therefore should be used selectively according to the application occasion.%在硅酸盐体系中添加钼酸钠,对比研究不同电压下钼酸钠对AZ91D镁合金微弧氧化膜层耐蚀性的影响.通过TT260涂层测厚仪、SEM和XRD分别检测了膜层厚度、膜层表面形貌和物相组成.采用点滴和电化学实验评估了膜层的耐蚀性能.结果表明:电解液中加入Na2MoO4后,膜层厚度变化不大,膜层点滴耐蚀性有所降低,但电化学耐蚀性呈增加趋势.在高电压下,添加0.42 g/L Na2MoO4获得的膜层耐蚀性最佳,比低电压下的高约1个数量级,比无添加剂时的高出31倍,比基体高约2个数量级.同时,Na2MoO4的加入,可在AZ91D镁合金表面制得棕色系的膜层,起显色作用的物质是MoO2,该物相徼溶于HNO3,但在电化学测试的NaC1介质中化学性质稳定,敌可根据应用场合进行选择性使用.