AZ91D鎂合金微弧氧化膜生長方式的多維探討Multi-dimensional investigation on coating growth of micro arc oxidation on AZ91D magnesium alloys

在硅酸鹽體系電解液中對AZ91D鎂合金進行微弧氧化處理，使用電子外徑千分尺、渦流測厚儀、掃描電子顯微鏡(SEM)以及電子探針顯微分析儀(EPMA)對試樣尺寸、膜層厚度、微觀形貌及所含元素的分布進行檢測，采用分界區直接觀察法、全基體直接測量法和膜層宏觀測量計算法3種方法研究膜層的生長方式。結果表明：第一種方法從膜層截面中直接觀察到鎂合金微弧氧化膜的確存在向內、向外生長的現象，為膜層的生長方式提供了直觀的證據；第二種方法直接、直觀地對基體和膜層的尺寸變化同時進行觀察與測量，同樣揭示存在膜層同時向內、向外生長的現象，且膜層向外的生長速率大于向內的；第3種方法的結果再次表明膜層存在向內、向外生長的現象，并且不同時間下膜層向外生長的尺寸均大于向內的尺寸，但膜層整體的生長速率逐步降低。

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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