采用扫描电镜、X射线衍射方法对Mg合金AZ91D在城市大气中的腐蚀层形貌, 腐蚀产物进行了分析和研究. 结果表明：腐蚀初期在材料表面生成一层Mg(OH)2薄膜, 随着腐蚀的不断进行, 膜增厚并开裂, 最终形成网状结构. 在裂纹处水蒸气容易凝聚, 腐蚀性气体及盐粒容易吸附, 且裂纹或缝隙为氧的扩散提供了通道, 造成Mg合金局部腐蚀严重. 生成的腐蚀产物主要为Mg(OH)2, Al(OH)3, Mg2CO3(OH)2•3H2O和Mg2(OH)3Cl•4H2O, 这些微溶的腐蚀产物对基体起到了一定的保护作用, 从而在后期降低了Mg合金的腐蚀速率.
The surface morphology of corrosion layer, corrosion products and structure of rust layer for AZ91D magnesium alloy in natural city atmosphere were studied by SEM and XRD. The results show that Mg(OH)2 layer forms at the initial corrosion period, then film thickens and cracks appear with continued corrosion under cyclic wet/dry conditions, in the end these cracks develop to reticulate structure. The water vapour is easily condensed and the corrosives gases, salt particles are easily absorbed in the cracks. Meanwhile, the cracks provide the diffusion paths for oxygen and other corrosion pollutants into matrix, which results in severe local corrosion. The major corrosion products are Mg(OH)2, Al(OH)3, Mg2CO3(OH)2•3H2O and Mg2(OH)3Cl•4H2O, which plays a partial role in protecting the matrix, therefore slowing down the average corrosion rate of magnesium alloy in the latter periods.
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