Er元素对定向凝固Al-Zn-Mg-Cu-Zr合金微观组织和共晶相形貌的影响

采用定向凝固方法制备了Al-Zn-Mg-Cu-Zr-xEr（x=0，0.1，0.2，0.5，质量分数，%）4种合金棒。利用光学显微镜（OM）、电子探针（EPMA）、能谱分析（EDS）和其他方法研究了铸态合金的微观组织和第二相形貌。结果表明：Er元素能增加Al-Zn-Mg-Cu-Zr合金定向凝固组织的枝晶数量，并能减小合金的一次枝晶臂间距和二次枝晶臂间距。适量Er元素能减少合金第二相的含量并有利于形成圆形第二相。生成的Al₈Cu₄Er相会降低T相（AlZnMgCu）中的Cu含量，起到圆润T相边界的作用，改变了T相的形貌和内部结构，并且Al₈Cu₄Er相能充当T相的形核位置，使得一部分T相围绕该相生长。Er的添加会提高合金的显微硬度。

Effects of Er on the Microstructure and Eutectic Phase Morphology of Directionally Solidified Al-Zn-Mg-Cu-Zr Alloys

Four alloy rods of Al-Zn-Mg-Cu-Zr-xEr (x=0, 0.1, 0.2, 0.5, wt%) were prepared by directional solidification. The microstructure and second phase morphology of alloys were investigated by optical microscopy (OM), electron probe micro-analysis (EPMA), energy dispersive spectrometer (EDS) and other methods. The results indicate that Er element can increase the number of dendrites in the directional solidification structure of Al-Zn-Mg-Cu-Zr alloy, and reduce the primary dendrite arm spacing and secondary dendrite arm spacing of the alloy. A proper amount of Er element can reduce the content of second phase in the alloy and increase the tendency to form round second phase. The formation of Al₈Cu₄Er phase can reduce the Cu content in the T phase (AlZnMgCu phase), which plays a role of rounding the boundary of the T phase, and can change the morphology and internal structure of the T phase. The Al₈Cu₄Er phase serves as the nucleation position of the T phase, and part of the T phase grows around this phase. The addition of Er can improve the microhardness of the alloy.