均匀化处理对Mg-Nd-Zn-Zr合金组织及力学性能的影响

通过光学显微镜(OM)、差热分析(DTA)、X射线衍射分析(XRD)、扫描电镜(SEM)及拉伸试验等方法,研究了均匀化处理对Mg-2.3Nd-0.5Zn-0.5Zr合金组织及力学性能的影响。结果表明:铸态合金主要由α-Mg、条状Mg₁₂Nd相及花瓣状Zn-Zr相组成。经均匀化处理后,条状Mg₁₂Nd相逐渐溶入基体,晶内还存有部分花瓣状Zn-Zr相,合金最佳的均匀化处理工艺为505 ℃×6 h。经最佳均匀化处理后,晶界第二相溶入基体消除了裂纹源,伸长率提高了100%,合金断裂模式由铸态的脆性解理断裂转变为延性穿晶断裂,但第二相强化及细晶强化效果的弱化抵消了固溶强化作用,合金的抗拉强度、屈服强度略有提高。

Effect of homogenizing treatment on microstructure and mechanical properties of Mg-Nd-Zn-Zr alloy

Effect of homogenizing treatment on the microstructures and mechanical properties of Mg-2.3Nd-0.5Zn-0.5Zr alloy was investigated by optical microscopy(OM), differential thermal analysis(DTA), X-ray diffractometry(XRD), scanning electron microscopy(SEM) and tensile test. The results show that the as-cast alloy is composed mainly of α-Mg, strip-like Mg₁₂Nd phase and petaloid Zn-Zr phase. After homogenizing treatment, the strip-like Mg₁₂Nd phase gradually dissolves into the matrix, while there are also partial petaloid Zn-Zr phase within the grains. The best homogenizing treatment for the alloy is 505 ℃×6 h, which leads the secondary phase at grain boundary to dissolve into the matrix so that the elongation of the alloy increases by 100%, and the fracture mode of the alloy changes from the brittle cleavage fracture in as-cast state to the ductile transgranular fracture. However, such a process causes weakening of both the secondary phase strengthening and the grain refinement strengthening so that offsets the solid solution strengthening, which result in that the tensile strength and yield strength of the alloy increase slightly.