本文评价了镁合金两类微弧氧化（Microarc Oxidation-MAO）膜层的耐蚀性，并分析了其在5wt.%NaCl水溶液中的腐蚀失效机理。研究发现：磷酸盐系膜层（P-film）和硅酸盐系膜层（Si-film）均可极大提高AZ91D合金的耐蚀性能，但硅酸盐系膜层的耐蚀性要优于磷酸盐系膜层的耐蚀性；依据Si-film和P-film在在5wt.%NaCl溶液中不同浸泡时间的自腐蚀电位（OCP）、腐蚀形貌和交流阻抗谱（EIS）数据的变化，MAO膜层的腐蚀失效主要经历了以下四个阶段：溶液渗入多孔层的孔隙；一些孔隙内被腐蚀产物充满；微孔底部的阻挡层逐渐被腐蚀；阻挡层失效，腐蚀过程趋于稳定。
The corrosion resistance of the two types of microarc oxidation (MAO) coatings was evaluated by virtue of total immersion test and salt spray. Then the mechanism of the coating corrosion failure in 5wt.%NaCl aqueous solution was studied through the impedance and open-circuit potential (OCP) measurements. The results showed that both phosphate coating (P-film) and silicate coating (Si-film) could enhance the corrosion resistance of AZ91D alloy significantly and that the later was more effective. Based on the variations of OCP and corrosion morphology of P-film and Si-film immersed in 5wt.%NaCl aqueous solution with different time, the analytic results of electrochemical impedance spectroscopy (EIS) data for Si-film showed the corrosion failure process had experienced the following four steps: the rapid initial penetration of the solution into the porous outer layer; the filling of corrosion products in certain pores; the gradual corrosion of the barrier layer located in the bottom of pores; the stable corrosion process with the failure of barrier layer.
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