不同状态的Mg-6Gd-2Y合金的显微组织特征

Microstructure characteristics at different status of Mg-6Gd-2Y alloy

摘要:

综合运用OM、 XRD、FEGSEM和HRTEM手段分析了Mg-6Gd-2Y合金铸态、固溶态和时效态的显微组织特征及演变过程。Mg-6Gd-2Y合金铸态组织主要由α(Mg)和呈不连续网状的Mg5(Gd,Y)相组成，在紧邻Mg5(Gd,Y)处有少量非平衡凝固相Mg2(Gd,Y)；对合金进行520℃固溶处理，随固溶时间延长，半连续状Mg5(Gd,Y)相尺寸逐渐缩小，直至溶解，并在晶界形成大量细小fcc结构的富稀土相Mg (Gd,Y) 2，明显阻止了α(Mg)晶粒的长大；合金在175℃~225℃时效处理时，175℃时效硬化效果最明显，时效析出过程包括：时效初期(4-32h)，过饱和α(Mg)析出β″相；快速析出期(32-100h)，α(Mg)析出β′相，100h达到峰值时效，析出相为β″、β′相；过时效期区(>100h)，β′相尺寸逐渐增大，并转化成β1和向稳定的β相转变。

Abstract:

The microstructures evolution of the Mg-6Gd-2Y alloy were investigated deeply during homogenizing and then aging treatment by OM,SEM, EDS, XRD, HRTEM in this paper. It was found that the microstructure of the as-cast alloy mainly consisted of α(Mg) equiaxed grains and eutectic compound Mg5(Gd,Y) with some non-equilibrium particles Mg2(Gd,Y). With the solution time prolonging, the α(Mg) grains did not significantly grow. The size of semi-continuous Mg5(Gd,Y) eutectic compound was shrinked gradually, and disappeared finally. And many fine RE-rich particles (Mg (Gd,Y) 2) with fcc structure were formed in the grain boundaries, which prevented the growth of α(Mg) grains. Age-hardening of the alloy at 175℃ was most obvious. β" phase was precipitated from α(Mg) matrix in the early-aging period(4-32h). β'' phase was formed in the rapid-aging precipitation period(32-100h). β" and β'' phase were mainly precipitation in the α(Mg) at the peak-aging stage(100h). β'' phase was transitioned to β1 ,which was transformed to stable β phase gradually at the over-aging stage (after 100h).