研究不同尺寸的Mg?6Gd?3Y?1Zn?0.3Ag(质量分数,%)镁合金零件冷却后的腐蚀行为.小型零件冷却较快,其显微组织由镁基体和粗大的长周期堆垛有序结构(LPSO)相组成.大型零件冷却较慢,其显微组织除镁基体和粗大的LPSO相外,晶粒内部有薄片状LPSO相析出.析氢测试结果表明,大型零件的腐蚀速度高于小型零件.交流阻抗测试显示这是由于大型零件上的表面膜的保护能力较差.通过观察腐蚀后形貌发现,大型零件样品中晶粒内析出的LPSO相诱发更加严重的微区电偶腐蚀,加速样品表面保护膜的破坏.
The corrosion behaviour of Mg?6Gd?3Y?1Zn?0.3Ag (wt.%) alloy components with different sizes after cooling was investigated. The alloys in the small components (SC) cooled fast, which were composed ofα-Mg matrix and coarse long-period stacking ordered (LPSO) phases. The alloys in the large components (LC) cooled slowly, and there were thin lamellar LPSO phases precipitating inside the grains, except forα-Mg matrix and coarse LPSO phases. The hydrogen evolution test revealed that the corrosion rate of LC sample was higher than that of SC sample. Electrochemical impedance spectroscopy (EIS) test showed that the surface film on LC alloys provided worse protection. The corrosion morphologies indicated that the precipitation of the thin lamellar LPSO phases in LC sample caused severe micro-galvanic corrosion, which accelerated the rupture of the surface film.