镁合金微弧氧化陶瓷膜的微观结构、相成分和耐腐蚀性能

为获得耐腐蚀性优良的镁合金表面膜层,在含5 g/L硅酸钠、2 g/L磷酸钠和1 g/L氢氧化钠的复合溶液中,用自制设备对AZ91D镁合金进行了微弧氧化.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陶瓷膜的表面形貌、截面结构和相组成.结果表明:AZ91D 微弧氧化陶瓷膜由疏松层和致密层组成,疏松层陶瓷膜疏松,厚度较大,且存在一些孔洞;致密层陶瓷膜与基体金属结合紧密,陶瓷膜主要由MgO,Mg2SiO4,Mg3(PO4)2和MgAl2O4组成.在3.5%的NaCl溶液中,微弧氧化陶瓷膜的自腐蚀电位为-1 390 mV,而镁合金基体的为-1 540 mV,表明经微弧氧化处理后AZ91D 镁合金的耐蚀性有较大提高.

Microstructure and Phase Composition and Corrosion Resistance of Micro-Arc Oxidation Ceramic Coating on AZ91D Magnesium Alloy

AZ91D magnesium alloys were anodized in an electrolyte solution containing 5 g/L sodium silicate,2 g/L sodium phosphate,and 1 g/L sodium hydroxide.The morphology,cross-sectional microstructure,and phase composition of the resulting micro-arc oxidation (MAO) ceramic coating formed on the surface of AZ91D magnesium alloy were analyzed by means of scanning electron microscopy and X-ray diffraction.The anticorrosion behavior of the MAO ceramic coating in aqueous solution containing 3.5% NaCl was examined using electrochemical method.Results showed that the MAO ceramic coating formed on the AZ91D magnesium alloy could be classified into a loose overcoating and a compact bulk coating,both composed of MgO,Mg-2SiO-4,Mg-3(PO-4)-2,and MgAl-2O-4.There existed some pores in the loose overcoating of a large thickness,while the compact bulk coating was well bonded to the AZ91D magnesium alloy matrix.Moreover,the MAO ceramic coating was capable of effectively increasing the corrosion resistance of the AZ91D magnesium alloy.