通过在0.6 mol/L NaCl溶液中浸泡实验, 研究重力砂型铸造镁合金AZ91D的耐腐蚀性能. 采用光学显微镜、扫描电镜和XRD观察和分析腐蚀后的合金与生成的氧化膜. 结果表明: 合金在溶液中的腐蚀以点蚀开始, 而后腐蚀介质通过点蚀坑向基体内部扩展; 氧化膜的成分随着腐蚀时间的延长不断变化; 氧化膜的晶界或缺陷处薄弱, 易开裂, 成为进一步腐蚀的通道; 随着腐蚀的发展, 氧化膜逐渐增厚, 腐蚀速率呈下降趋势; 由腐蚀速率的变化可以推测出不同成分的氧化膜的电极电位由里到外是逐渐上升的.
The corrosion performance of AZ91D magnesium alloy prepared by gravity sand casting was investigated in 0.6 mol/L NaCl solution. The corroded alloy and the formed oxide scales were examined by means of OM, SEM and XRD. The results showed that the corrosion of cast AZ91D in NaCl solution began with pitting, from which corrosion expanded over the surface and even pernetrated into the alloy substrate. The composition of the oxide cales formed during corrosion changed with time; oxides scales were apt to crack, which would be the starting point for further corrosion. With the development of corrosion, oxide scale thickened gradually, and the corrosion rate became lower. From the variation of of corrosion rate with time, it could be speculated that electrode potential of local sites was gradually increased from interior to its surface across the oxide scale with changing compositions.