AZ91D镁合金微弧氧化膜生长方式的多维探讨Multi-dimensional investigation on coating growth of micro arc oxidation on AZ91D magnesium alloys

在硅酸盐体系电解液中对AZ91D镁合金进行微弧氧化处理，使用电子外径千分尺、涡流测厚仪、扫描电子显微镜(SEM)以及电子探针显微分析仪(EPMA)对试样尺寸、膜层厚度、微观形貌及所含元素的分布进行检测，采用分界区直接观察法、全基体直接测量法和膜层宏观测量计算法3种方法研究膜层的生长方式。结果表明：第一种方法从膜层截面中直接观察到镁合金微弧氧化膜的确存在向内、向外生长的现象，为膜层的生长方式提供了直观的证据；第二种方法直接、直观地对基体和膜层的尺寸变化同时进行观察与测量，同样揭示存在膜层同时向内、向外生长的现象，且膜层向外的生长速率大于向内的；第3种方法的结果再次表明膜层存在向内、向外生长的现象，并且不同时间下膜层向外生长的尺寸均大于向内的尺寸，但膜层整体的生长速率逐步降低。

AZ91D magnesium alloys were treated by micro arc oxidation (MAO) in silicate-containing electrolyte. The sample dimension, thickness, morphology and element distribution of the coatings were examined by micrometer with electronic digital display, thickness tester, scanning electron microscope (SEM) and electron-probe micro analyzer (EPMA), respectively. The coating growth was investigated by three methods, containing directly observing the boundary area, macroscopically calculating the coating and directly measuring the whole substrate. The results show a phenomenon that the coatings growing inward and outward is observed intuitively in cross-section morphology of the MAO coating on magnesium alloys through the first method, and it proves the most intuitive evidence to illustrate how the coating grows. By the second method, dimensional changes of the substrates and the coatings can be observed and measured visually and the results also show that the coatings grow inward and outward at the same time, with lager grow rate outward compared with that of inward. The results of the third method once again show the coatings grow inward and outward simultaneously and the dimensions growing outward is lager than that of inward under different times, but the growth rate of the whole coating gradually reduces.

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