Mg-Gd-Zn系合金显微组织与相分析

Microstructure and Phase Analysis of Mg-Gd-Zn Alloys

为了研究Mg-Zn-Gd系合金中的相组成,采用热力学计算软件Pandat和Mg热力学数据库,外推计算了Mg-Gd-Zn系合金富镁角的水平截面图与垂直截面图,用Mg-6Gd-2Zn和Mg-6Gd-4Zn两种合金对该外推相图进行验证和修正,并在200℃下对该铸态合金保温480 h进行平衡处理,用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)及差热分析(DSC)对该平衡处理后的合金的平衡相组成及凝固过程的相变温度点进行分析。通过计算相图可知Mg-Gd-Zn系合金富镁角的平衡组织为α-Mg,Mg5Gd,MgZn三种平衡相;通过XRD可知该系合金中主要有α-Mg,Mg5Gd,MgZn 3种平衡相;通过DSC可知,Mg-6Gd-2Zn与Mg-6Gd-4Zn合金的液相线、固相线及过饱和固溶体析出相的相变温度的实验测定值与计算值误差分别为1.92%,4.99%,3.68%和0.05%,3.67%,0.16%,说明计算相图得到的相与XRD,DSC实验结果测得的相相符,证明此数据库外延计算相图可以使用;通过SEM照片及EDS分析可知Mg-Zn-Gd合金晶界处有板块状的Mg5(Gd,Zn)化合物与颗粒状Mg(Gd,Zn)化合物;通过计算得到的Mg-Gd-Zn系平衡相图的平衡组织为α-Mg+Mg5Gd+MgZn,而修正后的平衡组织为α-Mg+Mg5(Gd,Zn)+Mg(Gd,Zn)。

The composition of Mg-Zn-Gd alloys was researched. The horizontal cross-sectional and vertical cross-sectional phase diagrams of Mg-Gd-Zn alloys in Mg-rich corner were calculated with extrapolation method in detail by phase diagram calculation software Pandat and thermodynamic database for Mg alloys. The extrapolation phase diagrams were verified and corrected with Mg-6Gd-2Zn and Mg-6Gd-4Zn alloys, which were proceeded by equilibrium heat treatment at 200 ℃ for 480 h. The equilibrium phase composition and the phase transition temperature during solidification process for these two alloys were analyzed by the methods of optical microscope （ OM）, scanning electron microscopy （ SEM ）, X-ray diffraction （ XRD ） and differential scanning calorimetry （ DSC ）. The results of calculation phase in Mg-rich comer showed that the equilibrium phase was α-Mg, Mgs Gd, MgZn, which was consisted with the test resuits of XRD. The test result of DSC was the same with that of calculation phase diagram. The relative error of the calculated temperature and experimental temperature of liquid line, solidus and supersaturated solid solution precipitation phase were 1.92%, 4. 99%, 3.68% and 0.05%, 3.67%, 0.16% for Mg-6Gd-2Zn and Mg-6Gd-4Zn, respectively. The calculated phase diagram was consistent with experimental results of XRD and DSC, which proved that this extrapolation calculated phase diagram was available. The lath- shaped Mgs （Gd, Zn） compound and the graininess-shapod Mg（ Gd, Zn） compound distributed along the grain boundaries in Mg-Gd- Zn alloy were observed by SEM picture and EDS results. The equilibrium phase of calculation equilibrium phase diagram of Mg-Gd-Zn was amended from α-Mg ＋ Mg5C, d ＋ MgZn to α-Mg ＋ Mgs （ Gd, Zn） ＋ Mg（ Gd, Zn）.