电解质对AZ91D镁合金微弧氧化的影响

Effects of electrolyte on microarc oxidation of AZ91D magnesium alloy

在Na2SiO3和NaAlO2为主成膜剂的硅铝复合电解液中,利用交流脉冲电源对AZ91D镁合金进行微弧氧化处理,研究主成膜剂含量的变化对微弧氧化过程及膜层特性的影响规律。利用扫描电镜(SEM)和膜层测厚仪分别研究了膜层的微观形貌和膜层厚度,通过电化学阻抗谱(EIS)测试膜层在3.5%NaCl中性溶液中的耐蚀性能。结果表明,随着主成膜剂含量的增加,微弧氧化过程中起弧电压和终止电压均呈下降的变化趋势,而膜层耐蚀性则基本呈先增大后降低的变化趋势,膜厚的变化趋势与其耐蚀性一致;Na2SiO3含量的变化对膜层内部致密层和外部疏松层的耐蚀性均有影响,而NaAlO2含量的变化则主要影响膜层内部致密层的耐蚀性;适量的主成膜剂含量是获得致密耐蚀膜层的关键。

Microarc oxidation(MAO) process was conducted on AZ91D magnesium alloy in a composite electrolyte composed of Na2SiO3,NaAlO2 and some additives by AC pulse electrical source.Morphology and thickness of the coatings were investigated by scanning electron microscopy(SEM) and layer thickness meter.Corrosion resistance of the coatings in 3.5%NaCl neutral solution was evaluated by electrochemical impedance spectroscopy(EIS).The results show that striking voltage and final voltage decrease gradually with the increasing of the main components such as sodium silicate(Na2SiO3) and sodium aluminate(NaAlO2) in the electrolyte during the MAO process.With the increasing of main components in the electrolyte,corrosion resistance of the coatings increases first and then decreases gradually.The variation trend of coating thickness is the same as that of corrosion resistance.The corrosion resistance of both the inner dense layer and the outer loose layer are influenced by the concentration of Na2SiO3,and the concentration of NaAlO2 in the electrolyte mainly affects the corrosion resistance of the inner dense layer.Compact coatings with good corrosion resistance can be prepared only in an electrolyte with a good amount of main components.