均匀化处理对Mg-13Gd-3.5Y-2Zn-0.5Zr镁合金组织和力学性能的影响

对Mg-13Gd-3.5Y-2Zn-0.5Zr镁合金铸锭进行均匀化处理,温度为505～525℃,时间为4～24h,并采用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和万能材料试验机等检测手段分析均匀化处理前后合金微观组织和力学性能的变化。结果表明:均匀化处理后,原始组织中网状分布共晶化合物转化成晶界处不连续分布的块状LPSO相,离散分布的方块状富稀土相溶解。力学性能测试显示,铸态镁合金的抗拉强度为172.9MPa,伸长率为1.8%,经过均匀化处理后合金的力学性能得到提高,在515℃/16h均匀化制度下,合金室温抗拉强度为212.3MPa,伸长率为3.1%;在200℃下抗拉强度为237.2MPa,伸长率为9.7%,性能达到最佳。断口扫描显示,铸态合金是以撕裂棱与解理台阶为主的解理脆性断裂,均匀化处理后的合金中出现小而浅的韧窝,但仍然是以解理台阶为主的准解理断裂,塑性提高有限,长程有序相可成为裂纹的萌生源。

Effect of homogenization treatment on microstructure and mechanical properties of Mg-13Gd-3.5Y-2Zn-0.5Zr magnesium alloy

Homogenization heat treatment on the as-cast Mg-13Gd- 3.5Y-2Zn-0.5Zr magnesium alloy was carried out with the temperature range of 505-525℃ and the time range of 4-24h. Optical microscope (OM), scanning electron microscope(SEM), X-ray diffractometer(XRD) and universal material experiment machine were used to analysize the changes of microstructure evolution and mechanical property before and after homogenization. The results show that the reticular eutectic compounds in initial grain structure are transformed into discontinuous bulk-shaped LPSO (long-period stacking ordered) phases at the grain boundary and the discrete distribution of the square- shaped rich rare-earth phases dissolved. The mechanical properties test results show that the ultimate tensile strength and the elongation of the cast magnesium alloy are172.9MPa and1.8%, respectively. The mechanical properties of the alloy are improved after homogenization, the ultimate tensile strength of room temperature is212.3MPa and the elongation is 3.1% under the homogenization of 515℃/16h. At the same time, the ultimate tensile strength of high temperature at200℃ reaches the highest237.2MPa and the elongation is 9.7%. The fracture microstructure of as-cast alloy indicates that the fracture is cleavage brittle fracture dominated by tearing edges and cleavage steps, small and shallow dimples occur in the alloy after homogenization treatment, but is still quasi-cleavage fracture dominated by cleavege steps, and limited plasticity is improved. Meanwhile, LPSO phase can be the crack initiation source.