微弧氧化增强镁合金钼酸盐转化膜层的制备

目的提高钼酸盐转化膜的耐腐蚀性能,制备微弧氧化增强的钼酸盐膜层。方法采用化学转化法和微弧氧化法在AZ91D镁合金表面制备钼酸盐转化膜、微弧氧化膜和微弧氧化增强的钼酸盐膜层,研究了膜层的电化学行为和腐蚀失重情况,利用SEM、EDS、XRD和激光共聚焦显微镜对膜层的表面形貌、元素组成、物相组成和粗糙度进行分析。结果 XRD分析表明,钼酸盐膜层经过微弧氧化处理后,所得膜层较微弧氧化膜层多出新相MoSi_2。钼酸盐转化膜层经过微弧氧化处理后,相比于微弧氧化膜层,表面变得平整光滑,孔洞微粒变小,粗糙度降低。钼酸盐转化膜经过微弧氧化处理后,在3.5%NaCl溶液中浸泡48 h,膜层失重最低。通过电化学测试,微弧氧化增强钼酸盐膜层的腐蚀电位较钼酸盐转化膜的腐蚀电位正移0.643 V,较微弧氧化膜的腐蚀电位正移0.419 V,腐蚀电流密度较钼酸盐转化膜降低了3个数量级,较微弧氧化膜降低了1个数量级。结论钼酸盐转化膜经过微弧氧化处理后,膜层的耐腐蚀性能优于钼酸盐转化膜和微弧氧化膜,使镁合金的应用前景有所提高。

Preparation of Molybdate Conversion Coating on Magnesium Alloy Reinforced by Micro-arc Oxidation

The work aims to prepare the molybdate coating enhanced by micro-arc oxidation to improve the corrosion resistance of the molybdate conversion coating. Molybdate conversion coating, micro-arc oxidation coating and micro-arc oxidation enhanced molybdate coating were prepared on AZ91D magnesium alloys by chemical conversion and micro-arc oxidation. The electrochemical behavior and corrosion weight loss of the coatings were studied. SEM, EDS, XRD and laser confocal microscopy were used to analyze the surface morphology, element composition, phase composition and roughness of different conversion coatings. XRD analysis showed that after the micro-arc oxidation treatment of the molybdate coating, the obtained coating had a new phase MoSi2 compared with the micro-arc oxidation coating. After micro-arc oxidation treatment, compared to the micro-arc oxide coating, the surface of molybdate conversion coating became smooth, the pore particles became smaller, and the roughness reduced. After the molybdate conversion coating was subjected to micro-arc oxidation treatment, the obtained coating had the lowest weight loss when immersed in 3.5wt.% NaCl solution for 48 h. Through electrochemical tests, the corrosion potential of molybdate conversion coating enhanced by micro-arc oxidation was 0.643 V higher than that of molybdate conversion coating, and 0.419 V higher than that micro-arc oxidation coating. The corrosion current density decreased by three orders of magnitude compared with molybdate conversion coating and by one order of magnitude compared with micro-arc oxidation coating. The corrosion resistance of molybdate conversion coatings treated by micro-arc oxidation is better than that of molybdate conversion coatings and micro-arc oxidation coatings, thus improving the application prospects of magnesium alloys.