Improvement of corrosion resistance of AZ91D magnesium alloy by gadolinium addition
(1.湖北省武汉市武汉大学资源与环境科学学院
2.上海市科学院上海微系统与信息技术研究所
3.Shanghai Institute of Microsystem and Information Technology,Chinese Academy of Sciences, Shanghai 200050, China
4.School of Resource and Environmental Science, Wuhan University, Wuhan 430072, China)
2.上海市科学院上海微系统与信息技术研究所
3.Shanghai Institute of Microsystem and Information Technology,Chinese Academy of Sciences, Shanghai 200050, China
4.School of Resource and Environmental Science, Wuhan University, Wuhan 430072, China)
Abstract: Based on the previous investigation on beneficial introduction of holmium into magnesium alloy, the effect of gadolinium, an adjacent rare earth element, on corrosion resistance was examined. The corrosion behavior of two Mg-9Al-Gd alloys (Mg-9Al-0.45Gd and Mg-9Al-1.43Gd) was evaluated and compared with that of Mg-9Al alloy without Gd by means of specimen mass loss and hydrogen evolution in 3.5% NaCl solution saturated with Mg(OH)2. The Gd-containing alloys exhibit enhanced corrosion resistance with respect to the plain Mg-9Al alloy. The microstructures of Mg-9Al alloy and Mg-9Al-0.45 Gd alloy were observed by electron probe microanalysis (EPMA) and energy dispersion spectroscopy (EDS). The alloys with Gd addition show a microstructure characterized by α phase solid solution, surrounded by minor amount of β phase and more grain-like Gd-containing phase. To illustrate the involved mechanism their polarization curves were recorded. The electrochemical investigations reveal that Gd addition shifts the corrosion potential of the alloy towards active, as Gd containing phase is more active and hence less cathodic. As a result, the micro-galvanic corrosion is suppressed. Moreover corrosion product films formed on the Gd containing alloys are more compact and provide a better protective effectiveness than that on the alloy without Gd against corrosion. Repassivation measurements in mixture solution of 0.21 mol/L K2CrO4+0.6 mol/L NaCl also verify the beneficial role of Gd addition. Based on the present preliminary analysis, both the deposited Gd-containing phases and corrosion product films are believed to be responsible for the improved corrosion behaviour due to Gd addition.
Key words: AZ91D alloy; magnesium alloy; corrosion; gadolinium; rare earth