轧态Mg-Gd-Y-Zr合金显微组织及耐腐蚀性能研究

Microstructure and corrosion resistance of as-rolled Mg-Gd-Y-Zr alloy

用金相显微镜(OM)、扫描电镜(SEM)、能谱分析(EDS)等分析Mg-Gd-Y-Zr合金的显微组织;观察轧态合金在质量分数为3.5%NaCl溶液浸泡前后腐蚀形貌变化及相在腐蚀过程的作用。用腐蚀析氢试验、动电位极化测试分析轧态合金在不同时间的耐蚀性。对比Mg-Gd-Y-Zr合金铸态、轧态的耐腐蚀性能差异。结果表明:铸态组织由α-Mg基体和不连续分布于晶界的树枝状第二相构成,均匀化退火使树枝状第二相回溶,晶粒未明显长大,轧制变形使残留的方块状富Gd相尺寸变小;方块状富Gd相与基体相形成电极电位差,在腐蚀过程作为微阴极不溶解,α-基体相优先腐蚀溶解,腐蚀产物为针絮状的MgO;轧态Mg-Gd-Y-Zr合金在质量分数为3.5%NaCl溶液浸泡24 h的平均腐蚀速率为6.95095 mm/a。轧态合金中富Gd第二相总量少,尺寸小,与基体的微电偶腐蚀比铸态合金更弱,表面氧化膜保护性更好,在12 h自腐蚀电位最正(-1.54991 V),自腐蚀电流密度最小(1.51593×10-5A/cm2)。

The microstructures of Mg-Gd-Y-Zr magnesium alloy were studied by means of optical microscope(OM),scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS).The morphologies of the as-rolled Mg-Gd-Y-Zr alloy before and after immersion in 3.5%NaCl solution and the effect of phase during the corrosion process were observed.The hydrogenation test and polarization curves were used to analyze the corrosion resistance of magnesium alloy at different times.The corrosion resistance of the as-cast and as-rolled Mg-Gd-Y-Zr alloy was compared.The results show that the as-cast microstructure is consisted ofα-Mg matrix and the dendritic second phase that is discontinuously distributed at the grain boundaries.Homogenization annealing causes the dendritic second phase to dissolve back,the grains do not grow significantly,and the rolling deformation reduces the size of the residual block-like Gd-rich phase.The second phase of the Gd-rich phase forms an electrode potential difference with the matrix phase,and accelerates the surrounding matrix corrosion as a microcathode during the etching process,and the corrosion product is MgO.The average corrosion rate of the as-rolled Mg-Gd-Y-Zr alloy in the 3.5%NaCl solution for 24 h is 6.95095 mm/a.The total amount of Gd-rich phase in the as-rolled alloy is less,the size is smaller,the micro-galvanic corrosion with the matrix is weaker than that of the as-cast alloy,and the surface oxide film is more protective.Ecorris the most positive at 12 h(-1.54991 V),icorris the smallest(1.51593×10-5 A/cm2).