触变成型镁合金铸件热处理显微组织的演变

通过金相显微镜、SEM及XRD等观察手段研究了触变成型AZ91D镁合金铸件固溶、时效处理时显微组织的演变。结果表明:触变成型AZ91D镁合金在415℃时固溶处理时β相溶解入α-Mg固溶体的速度比高压压铸的快。在固溶处理初期,铝元素从β相扩散至块状初生α-Mg相,导致块状初生α-Mg晶粒周围形成富铝晕圈。时效处理时,触变成型铸件在5h左右硬度达到峰值,高压压铸铸件在12h左右达到峰值。触变成型铸件时效析出方式存在片层状不连续析出和针状连续析出两种。

Effect of heat treatment on microstructure of thixoformed AZ91D magnesium alloy

Microstructure and mechanical properties of a thixoformed AZ91D magnesium alloy in as-cast and heat treatment conditions were characterised by means of optical microscope(OM),scanning electron microscopy(SEM),XRD and hardness tests.The results show that the thixoformed AZ91D magnesium alloy exhibits a faster β phase dissolution rate than that in the high pressure die-cast alloy under solution treatment at 415 ℃.Al-rich halos are observed at the early stage of solution treatment because Al diffuses from the β phase to the primary α-Mg phase.During aging at 216 ℃,the thixoformed AZ91D magnesium alloy reaches its peak hardness at about 5 h while the high pressure die-cast alloy at 12 h.Both discontinuous and continuous precipitates of the β phase in the thixoformed alloy are observed.