T4和T6热处理对Mg-2.5Zn-1.5Ca-0.22Zr合金组织和硬度的影响

采用光学显微镜、扫描电镜和显微硬度仪等研究了T4和T6热处理对Mg-2.5Zn-1.5Ca-0.22Zr镁合金显微组织及硬度的影响。结果表明:Mg-2.5Zn-1.5Ca-0.22Zr镁合金经T4热处理之后,网状结构的β-Ca2Mg6Zn3相逐渐分解并转变为不规则的团聚的块状结构,MgZn2相逐渐溶解于α-Mg基体中,硬度比铸态时显著提高,达到63.87 HV;经过不同时间的T6热处理之后,MgZn2相从α-Mg基体中重新析出,球状的Mg2Ca中间化合物均匀的分布于晶粒内且发生明显长大。随着时效时间的延长,MgZn2相增多,对位错的钉扎增强,合金的硬度提高,在"峰时效"时的硬度达到64.97 HV。410℃×24 h固溶处理后150℃×8 h时效处理为Mg-2.5Zn-1.5Ca-0.22Zr镁合金的最佳热处理工艺。

Effect of T4 and T6 treatment on microstructure and microhardness of Mg-2.5Zn-1.5Ca-0.22Zr alloy

The effects of T4 and T6 heat treatment on microstructure and microhardness of Mg-2.5 Zn-1.5 Ca-0.22 Zr alloy were studied by means of optical microscope, scanning electron microscopy and microhardness tester. The results show that after solution treatment at 410 ℃ for different time, the network structure of β-Ca2Mg6Zn3 phase of the Mg-2.5 Zn-1.5 Ca-0.22 Zr alloy is gradually decomposed and transformed into a block-like structure with irregular aggregates, the MgZn2 phase is gradually dissolved in the α-Mg matrix, the hardness is obviously higher than that of the as-cast alloy, which is 63.87 HV. After aging at 150 ℃ for different time, the MgZn2 phase is re-precipitated from the α-Mg matrix, and the spherical Mg2Ca intermediate compound is uniformly distributed in the grains and grows obviously. With the increase of aging time, the amount of the MgZn2 phase increases, the pinning effect on the dislocation is enhanced, the hardness of the alloy increases, which is 64.97 HV at "peak aging". The optimum heat treatment process for the Mg-2.5 Zn-1.5 Ca-0.22 Zr alloy is as follows: solution treatment at 410 ℃ for 24 h and then aging at 150 ℃ for 8 h.