利用光学显微镜(Optical microscope,OM)、X射线衍射仪(X-ray diffractometer,XRD)、扫描电子显微镜(Scanning electron microscope,SEM)、能谱分析仪(Energy dispersive spectrometer,EDS)、透射电镜(Transmission electron microscope,TEM)和电子万能试验机等手段对传统砂型重力铸造方法制备的EV31A合金的显微组织和性能进行了深入研究.实验结果表明:铸态EV31A合金的显微组织由α-Mg和α-Mg+Mg41(Nd0.9Gd0.1)5共晶相组成,由于稀土元素含量较少,共晶反应发生在α-Mg结晶后期,表现为除少量固溶于α-Mg基体中,含稀土元素的Mg41(Nd0.9Gd0.1)5相主要分布在α-Mg的晶界处.Mg41(Nd0.9Gd0.1)5相为bcc结构,晶格常数为0.285 nm,呈鱼骨状,尺寸在数十微米.合金中α-Mg基体的晶粒尺寸为56.8 μm.EV31A铸态合金的抗拉强度、屈服强度和延伸率分别为207 MPa、124 MPa和7.0%.合金具有优异力学性能主要归因于Zr元素所带来的细晶强化,Gd、Nd、Zr等溶质原子的固溶强化,共晶Mg41(Nd0.9,Gd0.1)5相所带来的第二相强化等多种强化方式的协同作用.
Abstract
The microstructure and mechanical properties of as-cast EV31A alloys are investigated by using optical microscope(OM),X-ray diffractometer(XRD),scanning electron microscope(SEM),energy dispersive spectrometer(EDS),transmission electron microscope(TEM),and electronic universal testing machine.Experimental results show that the microstructure of as-cast EV31A alloys is the α-Mg matrix and Mg41(Nd0.9Gd0.1)5 eutectic phase.Due to the low content of rare earth elements,the eutectic reaction occurs in the late stage of α-Mg crystallization,manifested as the Mg41(Nd0.9Gd0.1)5 phase containing rare earth elements mainly distributed at the grain boundaries of α-Mg,except for a small amount of solid solution in the α-Mg matrix.The Mg41(Nd0.9Gd0.1)5 phase has a bcc structure with a lattice constant of 0.285 nm.The grain size of α-Mg in the alloy is 56.8 μm.The ultimate tensile strength,yield strength and elongation are 207 MPa,124 MPa and 7.0%,respectively.The excellent mechanical properties of alloys are mainly attributed to the fine grain strengthening brought by Zr,solid solution strengthening of solute atoms such as Gd,Nd,Zr,etc,and the synergistic effect of multiple strengthening methods such as second phase strengthening brought by eutectic Mg41(Nd0.9,Gd0.1)5 phase.
维普
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