固溶时间对ZA72镁合金显微组织及力学性能的影响

摘要

利用光学显微镜、X射线衍射仪、扫描电镜和力学万能试验机研究ZA72镁合金在不同固溶时间下T6处理后的显微组织和力学性能.结果表明:ZA72镁合金主要由α-Mg和分布在晶界的连续粗大的Mg32(Al,Zn)49和Mg7Zn3相组成,经过固溶处理后第二相呈细小的颗粒状分布在晶界和晶粒上,随着固溶时间的增加,第二相的尺寸和数量逐渐减小；经T6处理后,细小、弥散的白色点状强化相在晶界和晶粒内部弥散析出,并且随着固溶时间的增加,析出相的数量增加；通过T6处理后合金的力学性能有了明显的改善,合金的抗拉强度和显微硬度随固溶时间的增加呈先上升后下降的趋势,其中在固溶28 h后抗拉强度出现峰值308 MPa,相对于铸态提高了52.4％.%The microstructure and mechanical properties of ZA72 magnesium alloy after T6 heat treatment with different solution times were investigated using optical microscope (OM), X-ray diffractometer (XRD), mechanical apparatus and scanning electron microscope (SEM). The results show that the ZA72 magnesium alloy mainly contains a-Mg, bulky Mg32(Al,Zn)49 and Mg7Zn3 phases which distribute on the grain boundary continuously. After T4 heat treatment, the second phases are converted to fine particles, meanwhile the size and amount have decreased gradually with the solution time increasing. The fine and dispersible white dots precipitates separate out at the grain boundary and grain internal, in addition that the amount of precipitates increase with the solution time extending. The mechanical properties of alloy are obviously improved after T6 heat treatment, the tensile strength and micro-hardness show the trend of arising first and descending later. When the solution time is 28 h, the tensile strength reaches the peak value of 308 Mpa, which increases by 52.4% compared with that of the as-cast alloy.