NaOH含量对AZ91D镁合金微弧氧化膜层微观结构和耐蚀性的影响

在由15 g/L Na2SiO3、12 g/L NaAlO2、3 g/L Na2B4O7、5 mL/L C3H8O3、5 g/L C6H5Na3O7及1~4 g/L NaOH组成的硅铝复合电解液中,利用微弧氧化技术在AZ91D镁合金基体上制备了一系列陶瓷膜层.利用扫描电镜、膜层测厚仪分别研究了陶瓷膜层的微观结构及厚度;采用全浸泡实验和交流阻抗实验测试了膜层在3.5%NaCl溶液中的耐蚀性能.结果表明：随着NaOH含量的增加,微弧氧化过程中的起弧电压和终止电压均呈线性下降;膜层的耐蚀性随着NaOH含量的增加先提高后降低,膜厚的变化趋势与其耐蚀性的变化趋势基本一致;NaOH含量的变化主要影响膜层内部致密层的耐蚀性能;当NaOH含量为2 g/L时,膜层最厚,膜层较致密,因而具有较好的耐蚀性能.

Effect of NaOH concentration on microstructure and corrosion resistance of MAO coatings fabricated on AZ91D magnesium alloy

Ceramic coatings were obtained on AZ91D magnesium alloy by microarc oxidation in a silicate-aluminate based composite electrolyte containing 15 g/L Na2SiO3,12 g/L NaAlO 2,3 g/L Na2B4O7,5 mL/L C3H8O3,5 g/L C6H5Na3O7 and 1~4 g/L NaOH. The morphology and thickness of ceramic coatings were exam- ined by scanning electron microscopy（ SEM） and layer thickness meter. The corrosion resistance of ceramic coatings in a 3. 5% NaCl neutral solution was evaluated by immersion test and electrochemical impedance spectroscopy（ EIS）. The results show that striking voltage and final voltage during the MAO process decrease gradually as the concentration of NaOH increases. With the increasing of NaOH concentration in the electrolyte,the corrosion resistance of coating increases first and then decreases gradually. The variation trend of coating thickness is the same as that of corrosion resistance. The concentration of NaOH in the electrolyte mainly affects the corrosion resistance of the inner dense layer. The coating obtained in the electrolyte containing 2 g/L NaOH exhibits a better corrosion resistance due to the relatively compact microstructure and thick coating.