交变方波电源参数对镁合金AZ91D微弧氧化的影响

Influence of electric parameters on MAO of AZ91D magnesium alloy using alternative square-wave power source

在碱性硼酸盐体系中,使用新型的交变方波电源在镁合金AZ91D上制备微弧氧化膜。用正交实验法研究电压、频率和占空比等电源参数对微弧氧化膜性能的影响。结果表明:微弧氧化膜的厚度随电压和占空比的升高而增厚,但随频率的升高而减薄。氧化膜的结构和形貌随电源参数的变化而变化,氧化膜上的孔隙和裂缝会随着电压和占空比的升高而增多。当电压低于120V时,只能得到薄而透明的氧化膜,氧化膜的主要成分为MgO,Al2O3,MgAl2O4和MgSiO3。在3.5%氯化钠溶液中,采用电化学阻抗谱和极化曲线检测了氧化膜的耐腐蚀性。结果表明,当电压、频率和占空比分别为140V,2000Hz和0.4时,微弧氧化膜的耐腐蚀性最好。

Micro-arc oxidation （MAO） process was carried out on AZ91D alloy in alkaline borate solution using an alternative square-wave power source with different parameters. The effects of voltage, frequency and duty cycle on the coatings were investigated by orthogonal experiment. It is found that the thickness of coatings increases with the increase of voltage and duty cycle, but decreases with the increase of frequency. The structure and morphology of the coatings also depend on voltage, frequency and duty cycle. The coatings become more porous and crack with increasing voltage and duty cycle. The coating is thin and transparent when the voltage is lower than 120 V. The corrosion resistances of different coatings were evaluated by polarization curves and electrochemical impedance spectroscopy （EIS） in 3.5% NaCl （mass fraction） solution. When the optimized values of voltage, frequency and duty cycle are 140 V, 2 000 Hz and 0.4, respectively, the anodic coating shows the best corrosion resistance.