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

Effects of heat-treatment technology on microstructure and mechanical properties of Mg-6Zn-2Sm-0.4Zr magnesium alloy

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+Mg_2Zn_3+Mg_(41)Sm_5)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%。

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 matrixα-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 44MPa and 90.80% compared with those of the as-cast alloy,respectively.