合金元素对Mg-Zn-Gd合金组织和力学性能的影响

Effects of Alloying Elements on the Microstructure and Mechanical Properties of Mg-Zn-Gd Alloys

采用金相显微分析、X射线衍射、扫描电子显微镜和室温拉伸试验,研究了合金元素Zn、Gd对Mg-Zn-Gd合金铸态组织和力学性能的影响。结果表明,当Zn含量不变时,随着Gd含量的增加,合金中的第二相依次从准晶相(I相)+Mg7Zn3相、I相到I相+W相转变,二次枝晶臂间距明显减小,晶粒细化,晶间组织也由颗粒状、细线状向封闭的网状转变;当保持x(Zn)/x(Gd)=5.8不变时,合金第二相的组成不变,枝晶相分布更加细密,第二相也随之增多。拉伸测试表明,当Zn含量不变时,随着Gd含量的增加,合金的抗拉强度和伸长率均增加,但屈服强度先升高后降低;同比例增加Zn、Gd的含量,合金的强度升高,伸长率降低。

Effects of Zn and Gd on the as-cast microstructure and mechanical properties of Mg-Zn-Gd alloys were investigated by menas of optical microscope(OM),XRD(X-ray diffraction),SEM(scanning electron microscope) and tensile testing at room temperature.The results reveal that Gd content plays an important role in the phase constitution of the alloys.When given a fixed Zn content,with the increase of Gd content,the second phase transformation was observed as follows:Mg7Zn3 phase +Iconsahedral quasicrystalline phase(I phase)→I phase →I phase +W phase.Meanwhile,the secondary dendrite arm is evidently decreased and morphology of the interdendrite is evolved from particle into needle-like structure and then into closed net-like structure.When the atomic ratio of Zn to Gd keeps constant of 5.8,with increasing in total content of Zn and Gd contents,the second phase constituent sustains stable,however,the more fine dendrite phase is distributed into the microstructure with the increase of second phase volume fraction.Tensile testing indicates that when the Zn is given a fixed value,with increasing in Gd content,both the tensile strength and elongation of the alloy are improved,however,the yield strength is firstly increased and then decreased.In addition,when the atomic ratio of Zn to Gd keeps a constant value of 5.8,with increase of the total content Zn and Gd,the alloy exhibits higher strength and lower elongation.