热处理工艺对Mg-6Zn-2Sm-0.4Zr镁合金显微组织和力学性能的影响

摘要

A new type Mg-6Zn-2Sm-0.4Zr alloy was fabricated by adding 0.4%Zr and 2%Sm (mass fraction) in Mg-6Zn alloy, and the microstructure and mechanical properties of the cast alloy under the conditions of as-cast, solution and aging treatment were investigated by optical microscopy (OM), scanning electron microscopy (SEM) with equipped energy dispersive spectrometry (EDS), X-ray diffractometry (XRD), micro-hardness and mechanical tests. The results indicate that the as-cast alloy is mainly composed of matrix α-Mg, eutectic phases (α-Mg+Mg2Zn3+Mg41Sm5) with continuous or semi-continuous morphology distributed along grain boundaries and a few isolated particles inside grains. The alloy is solutionized at 440 ℃ and 450 ℃ for 12?36 h, with the increment of solution temperature and time, the solution effect gradually increases. When the alloy is treated at 450 ℃ for 28 h, the alloy exhibits relatively homogeneous microstructure and attains mechanical performance with ultimate tensile strength (UTS) of 230 MPa and elongation (EL) of 9.58%, respectively. After the alloy being aged at 200 ℃ for 6?48 h, the mechanical properties of alloy increase obviously, and the aging strengthening effect increases firstly and then decreases, the peak values of UTS (258 MPa) and EL (14.43%) of the alloy aged at 200 ℃ for 12 h are simultaneously obtained, which are increased by 44 MPa and 90.80%compared with those of the as-cast alloy, respectively.%通过在Mg-6Zn合金中添加0.4%Zr和2%Sm(质量分数)制备出一种新型Mg-6Zn-2Sm-0.4Zr合金;利用光学显微镜(OM)、扫描电镜(SEM)及能谱仪(EDS)、X射线衍射仪(XRD)、显微硬度及力学性能测试研究铸造Mg-6Zn-2Sm-0.4Zr合金在铸态、固溶、时效处理下的显微组织和力学性能的变化.结果表明:合金铸态组织主要由基体α-Mg、晶界处呈连续或半连续分布的(α-Mg+Mg2Zn3+Mg41Sm5)共晶和晶内孤立的点状相组成.合金在440和450℃固溶12~36 h时间范围内,随着时间和温度的增加,固溶效果逐渐增强.当在450℃固溶28 h时获得了较好的显微组织,抗拉强度为230 MPa,伸长率为9.58%.随后经200℃时效6~48 h后,合金的力学性能明显提高,时效强化效应随时间的延长呈先增加后减小的趋势,其中时效12 h时同时出现了抗拉强度和伸长率的峰值258 MPa和14.43%,比铸态的分别提高44 MPa和90.80%.