第二相在Mg-Gd-Y-Zr合金挤压棒超塑性变形中的作用

Effect of second phase on superplastic deformation of extruded rod of Mg-Gd-Y-Zr alloy

采用电子显微镜和XRD研究分析Mg-Gd-Y-Zr合金挤压棒材超塑性拉伸前后的微观组织及其超塑性机制。结果表明:在温度为450℃、应变速率为2×10-4s-1的变形条件下获得的挤压棒的最大伸长率为410%,应变速率敏感系数为0.54;合金表观变形激活能远高于镁的晶界扩散激活能或晶格扩散激活能,超塑性变形机制为晶格扩散控制的位错协调晶界滑动机制;微孔洞在基体/方形富稀土相界面处萌生,较软的不规则块状β相承受部分塑性变形,松弛了相界处应力集中。

The microstructures and superplastic behavior of the extruded rod of Mg-Gd-Y-Zr alloy before and after tensile were investigated and analyzed by microscopy and XRD. And tensile tests at various temperatures and strain rates were performed. The results show that the extruded rod exhibits the maximum elongation of 410% at 450 ℃ and 2×10^-4 s-1 and the corresponding strain rate sensitivity of 0.54. The apparent activation energy for the superplastic flow is much higher than the activation energy of grain boundary diffusion or lattice diffusion of magnesium. The high ductility is attributable to grain boundary sliding accommodated by dislocation motion assisted by lattice diffusion. The microstructural results show that the cavities nucleate at the interface between the matrix and the cuboidal Re-rich phase, and that the deformable β phase relaxes the stress concentration at the interface by bearing the partial plastic strain.