近年来，镁合金因比强度比刚度高、质量轻、延展性良好和高的导热性等诸多优点，被广泛地应用于汽车、航空、电子等领域。但是镁合金有个致命的缺点就是化学性质太活泼，极易在各种环境中被氧化，因此开发镁合金的防护技术对推进镁合金的工业化发展具有十分重要的意义和应用价值。 本文以AZ91D镁合金作为研究对象，采用正交实验和单因素实验，确认了钼酸盐转化液体系为：钼酸钠(NaMoO4 ) 30g/L，温度为50ºC，高锰酸钾(KMnO4 ) 8g/L，处理时间为40min，pH值为5.5。转化膜表面形貌为宽裂纹与窄裂纹镶嵌组合而成，EDS分析表明Mo、Mn含量在宽裂纹区分布多于窄裂纹区；耐点滴腐蚀实验表明转化膜试样比镁基体在腐蚀液中的耐蚀时间延长近11分钟；极化曲线和阻抗谱结果表明转化膜的自腐蚀电流密度为1.32×10-7A/cm2，比镁基体降低了2个数量级，极化电阻为1368.4Ω·cm2，是镁基体极化电阻的7倍。 在转化膜的基础上，采用化学转化与溶胶凝胶技术相结合的工艺，在镁合金转化膜上制备出了杂化涂层，形成复合膜层。复合膜层的结合力达到1级，涂层表面形貌致密均匀无裂纹，腐蚀电流密度比镁基体的降低了3个数量级，极化电阻达到3.03×104Ω·cm2。采用动电位极化和交流阻抗技术研究了转化膜和复合膜在NaCl溶液中的腐蚀行为。结果表明，转化膜和复合膜在浸泡后期都会出现感抗弧，表现出相似的电化学腐蚀行为，只是耐腐蚀的时间和程度相差较大，复合膜在3.5%NaCl溶液中的浸泡时间长达204h，而转化膜的浸泡时间只有42h。

In recent years, magnesium alloy is widely used in automobile, aviation, electronics and other fields because of its low density, high specific stiffness and strength ratio, good ductility and high thermal conductivity and so on. However, active chemical properties as a fatal weakness of magnesium alloy which is extremely easy to oxygen in the various circumstance. Therefore, the development of protection technology of magnesium alloy to promote the industrialization development of magnesium alloy has very important significance and application value. In this paper, AZ91D magnesium alloy,by using orthogonal experiment and single factor experiment confirmed the molybdate conversion solution system: sodium molybdate (NaMoO4) 30g/L, potassium permanganate (KMnO4) 8g/L, the temperature is 50 degrees centigrade, processing time is 40min with pH value of 5.5.Surface morphology of conversion film was based of wide and narrow crack, EDS analysis indicated that the concentration in the zone of wide cracks distributed more than narrow crack zone; resistance spot corrosion experiments showed that corrosion time of conversion film was longer nearly 11 minutes than magnesium matrix in the corrosion liquid; electrochemical test showed that corrosion current density of the conversion film which reached 1.32×10-7A/cm2 was lower two orders of magnitude than magnesium substrate and polarization resistance for 1368.4Ω·cm2 that was seven times higher than polarization resistance of the magnesium matrix . Based on the conversion film, combining the chemical conversion with sol-gel technology in magnesium alloy, hybrid organic coating were prepared on the conversion film forming a composite film.The results showed that combination ranking of the composite film was up to 1 level, surface morphology of coatings had no crack that was dense and uniform, the corrosion current density was lower 3 orders of magnitude than the magnesium substrate,the polarization resistance reached 3.03×104Ω·cm2. Corrosion behavior of conversion film and composite coating in NaCl solution was investigated by the polarization curves and electrochemical impedance spectroscopy. The results indicated that the conversion film and composite coating in the late immersion would generate inductive reactance arc, which showed similar electrochemical corrosion behavior.The difference was immersion time of composite film reached 204 hours but conversion film only 42 hours.