镁合金微弧氧化膜结构及耐蚀性的初步研究

空气中由于AZ91D镁合金耐腐蚀性差,影响实际应用.为了弄清腐蚀原因,增加应用效果,作者利用扫描电镜和X射线衍射分析了AZ91D镁合金表面微弧氧化膜的形貌、结构和相组成,并对氧化膜的耐蚀性作了初步试验分析.研究表明,AZ91D微弧氧化膜呈3层结构,外层氧化膜存在一些孔洞;中间层氧化膜疏松、具有较大厚度;内层氧化膜与基体金属结合紧密.氧化膜主要由MgO,MgSiO3,MgAl2O4,Mg3(PO4)2组成.经1周3%NaCl溶液浸泡试验,结果表明微弧氧化膜可以较大程度地提高AZ91D镁合金的耐蚀性,但氧化膜表面富含Si,P的颗粒是易发生腐蚀的电化学活性点,导致氧化膜发生局部腐蚀.

Microstructure and Corrosion Resistance of Microarc Oxidation Film on AZ91D Magnesium Alloy

Corrosion resistance of AZ91D magnesium alloy is weak in air. In order to reveal corrosion mechanism and improve performance, the morphology, nficrostructure and phase composition of microarc oxidation (MAO) film on AZ91D magnesium alloy were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Furthermore the corrosion resistance of film was tested. Results show that the MAd film on AZ91D magnesium alloy contains three layers that are outer layer, middle layer and inner layer. Some small discharge pores lie in the outer layer. The middle layer is loose and thick. Inner layer is combined to metal substrate tightly. The MAd film is mainly composed of MgO, MgSiO_3, MgAI_2O_4 and Mg_3 (PO_4)_2 compounds. The microarc oxidation is proved to improve corrosion resistance of AZ91D after three -week immersion in 3% NaCI solutinn. There exist pitting corrosion on the oxide film for ninny small particles containing Si and P element richly on the surface are electrochenfically active sites easy to corrode.