材料期刊网

    优化镁合金微弧氧化常用的Na₂SiO₃电解液并制备了白色陶瓷质微弧氧化膜，采用动电位极化曲线和电化学交流阻抗(EIS)等方法研究其防护性能.结果表明，与常用的Na₂SiO₃电解液制备的试样相比，优化的Na₂SiO₃电解液所制备试样的自腐蚀电流降低了3个数量级，并表现出较高的阻抗值；在3.5% NaCl溶液中浸泡发生点蚀的时间从24 h延长到240 h.SEM和XRD分析结果表明，在优化的Na₂SiO₃电解液中制备的AZ91D的陶瓷膜层孔隙减少，孔径也较小，且增加了低溶解度的Mg₅F₂(SiO₄)₂相和起钝化作用的MgAl₂O₄相.

    Plasma electrolytic oxidation of AZ91D magnesium alloy was studied in an optimized solution mainly containing Na₂SiO₃.The microstructure,phase constituents and elemental distribution of ceramic films were investigated by using scanning electron microscopy(SEM) and Xray diffraction(XRD).The corrosion resistance of the magnesium alloy with ceramic films were evaluated by potentiodynamic polarization curves and electrochemical impedance spectroscopy(EIS).The results indicated that I_corr of the magnesium alloy oxidized in the optimized solution was decreased by three orders of magnitude compared with that oxidized in the conventional solution.The polarization resistance of the magnesium alloy oxidized in the optimized solution was higher than that oxidized in the conventional solution,and the time for appearance of obvious corrosion pits during immersion in 3.5% NaCl solution was increased from 24 h for the sample oxidized in the conventional solution to 240 h for that oxidized in the optimized solution.The better corrosion resistance of the magnesium alloy oxidized in the optimized solution results from fewer defects,fewer pores,as well as higher content of the phase of Mg₅F₂(SiO₄)₂ with lower dissolubility and the MgAl₂O₄ with better passivity in the oxide film.