镁基复合材料保持了镁合金的优点，同时又具有高比强度和比刚度等特点，但是它比镁合金更容易腐蚀的特性严重限制了其应用。本文在磷酸盐和硅酸盐两种电解液体系中，对硅酸铝短纤维含量为20 vol.%和33 vol.%的Al2O3-SiO2(sf)/AZ91D镁基复合材料进行微弧氧化表面处理。对微弧氧化工艺参数进行了优化，并对比分析了AZ91D镁合金微弧氧化陶瓷膜的表面形貌、组织结构和性能，探讨了增强体对微弧氧化膜生长、腐蚀及磨损性能的影响，着重研究了微弧氧化处理前后镁合金及其复合材料的电化学腐蚀行为。在磷酸盐体系中，AZ91D和Al2O3-SiO2(sf)/AZ91D复合材料微弧氧化膜的主要组成相均是MgO晶态相，复合材料微弧氧化膜还含有少量的尖晶石相（MgAl2O4）和莫来石相（3Al2O3•2SiO2）。硅酸盐体系中，微弧氧化膜主要由MgO和Mg2SiO4相组成，复合材料氧化膜还含有少量的MgAl2O4相。两种电解液中生长的微弧氧化膜硬度较高，有较好的耐磨性。复合材料里的硅酸铝增强体参与了氧化膜的生长，它在微弧放电作用下逐渐熔解，从而保持了膜层完整性。在NaCl溶液中浸泡和中性盐雾试验表明，复合材料基体由点蚀发展为严重的局部腐蚀，最后整个表面遭到破坏，复合材料基体的腐蚀程度远大于AZ91D合金，而微弧氧化表面处理后复合材料的耐腐蚀能力明显提高。电化学阻抗谱研究表明，三种镁基材料在3.5 wt.% NaCl溶液中腐蚀机制相同，以镁与水的电化学反应方式进行。微弧氧化膜的腐蚀分为电解质溶液通过表面疏松层进入内部致密层和通过致密层到达膜/基界面引起基体腐蚀两个阶段，第二阶段为腐蚀速度控制步骤。各种腐蚀试验结果表明，微弧氧化处理可以有效地提高镁合金及其复合材料的耐腐蚀性能，膜层较厚且致密程度较高时抗腐蚀能力显著提高。Al2O3-SiO2(sf)/AZ91D复合材料在磷酸盐和硅酸盐两种电解液中生长的微弧氧化膜耐腐蚀性能都比相应的镁合金微弧氧化膜差，微弧氧化膜致密层较厚时镁合金和复合材料的耐蚀性比较接近。硅酸盐体系微弧氧化膜的性能总体优于磷酸盐体系。

In addition to the same advantages as magnesium alloys, magnesium matrix composites have high strength and stiffness to density ratios, however, they are more sensitive to corrosion than magnesium alloys due to the incorporation of reinforcements. In this thesis, ceramic coatings were prepared on 20 vol.% and 33 vol.% Al2O3-SiO2(sf)/AZ91D magnesium matrix composites by microarc oxidation (MAO) technique in phosphate electrolyte and silicate electrolyte. Oxidation parameters of microarc oxidation were optimized, then the surface morphology, microstructure and property of the coated composites were compared with the coated AZ91D magnesium alloys. At the same time, the influences of reinforced phase on growth process, corrosion resistance and tribological behaviors were disscussed. The electrochemical corrosion behaviors of magnesium and its composites before and after MAO surface treatment were emphatically analyzed. The MgO is a main constituent phase in MAO coatings obtained in phosphate electrolyte on AZ91D alloys and Al2O3-SiO2(sf)/AZ91D magnesium matrix composite, and a little spinel (MgAl2O4) and mullite (3Al2O3•2SiO2) phases were also found in the coatings on magnesium matrix composite. However, the coatings formed in silicate electrolyte mainly consist of MgO and Mg2SiO4 phases, and a small quantity of MgAl2O4 was also observed in the coatings on the composite. The MAO coatings prepared in the two electrolyte systems have much higher hardness, which display a high wear resistance. In microarc oxidation, the Al2O3-SiO2(sf) reinforcements take part in the growth of coatings, and are gradually melted to corporate into the coatings under microarc discharge, thus the integrality of MAO coatings is maintained. The immersion test in 3.5 wt.% NaCl solution and neutral salt spray test in 5.0 wt.% NaCl solution showed that the corrosion of Al2O3-SiO2(sf)/AZ91D composite substrates evolved from pitting to serious localized corrosion, and at last completed damage on the whole surface. It was found that the corrosion on the composite substrates was much more serious than that of AZ91D alloys. On the other hand, the corrosion resistance of coated Al2O3-SiO2(sf)/AZ91D composites by microarc oxidation were noticeably improved. Electrochemeical impedance spectroscopy (EIS) test implied that the three materials of AZ91D magnesium alloy and Al2O3-SiO2(sf)/AZ91D composites had a same corrosion mechanism in 3.5 wt.% NaCl solution, which electrochemical reaction was conducted by Mg and H2O. The corrosion process of MAO coatings may include two stages: the first stage was Cl- ions in solution enters the dense layer of coating from the porous outer layer, and the second stage was that Cl- ions reached the coatings/substrate interface through dense layer and resulted in base metal corrosion. The second stage controlled the corrosion rate of coated composites.All of corrosion tests indicated that microarc oxidation surface treatment, especially for a thick and dense coating, could significantly improve the corrosion resistance of magnesium alloy and their composites. It was also found that coated magnesium alloy in phosphate or silicate electrolyte has better corrosion resistance than coated Al2O3-SiO2(sf)/AZ91D composite, but their corrosion resistance was similar when they have a thick dense layer of coating. In general, coatings prepared in silicate electrolyte have better corrosion and wear resistance than that in phosphate electrolyte.