四硼酸钠对AZ91D镁合金微弧氧化膜特性的影响

Effects of Na_2B_4O_7·10H_2O on Characteristics of MAO Coatings Fabricated on AZ91D Magnesium Alloy

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、超景深光学显微镜分别研究了陶瓷膜层的微观形貌特征、厚度及表面粗糙度;采用交流阻抗谱测试了膜层在3.5%NaCl溶液中的耐蚀性能。结果表明,四硼酸钠质量浓度的变化对微弧氧化过程中的起弧电压和终止电压影响不大,适量的四硼酸钠可以稳定微弧氧化过程的控制电压;随着四硼酸钠质量浓度的增加,微弧氧化膜层的厚度先增加后降低,膜层表面粗糙度随着四硼酸钠质量浓度的增加呈先增加后降低的变化趋势;当四硼酸钠质量浓度为3g/L时,膜层较致密,表现出良好的耐蚀性能。

Ceramic coatings were prepared on AZ91D magnesium alloy by micro-arc oxidation in a sili- cate-aluminate based composite electrolyte with various NaEB4O7. 10H2O concentration. Morphology, thickness and surface roughness of the ceramic coatings were characterized by scanning electron microscopy（SEM） ,layer thickness meter and digital microscope respectively. Corrosion resistance of the coatings in 3.5 % NaC1 neutral solution were also evaluated by electrochemical impedance spectroscopy （EIS）. Results showed that NazB4O7 .10H2O concentration had little effect on striking voltage and final voltage of the MAO process, but proper Na2B4O7 · 10H2O concentration could stabilize the voltage. With increasing of the Na2 B4O7 · 10H2O concentration in electrolyte, thickness of the coatings increased at first and then decreased gradually, though the thickness variation was not obvious, and surface roughness of the coatings increased at first and then decreased also. EIS results also showed that corrosion resistance of the coatings increased at first and then decreased with increasing of the Na2B4O7 · 10H2O concentration. Under the Na2B4O7 · 10H2O concentration of 3 g/L,the coating was dense and compact, and had a best corrosion resistance.