通过差热分析, 测定了AZ81镁合金的相变温度点, 采用液淬方法得到了AZ81镁合金在相变点附近的组织, 采用光学显微镜、扫描电镜和能谱仪等对凝固行为和组织演变进行了分析。结果表明: AZ81镁合金的固液相变温度约为590 ℃, 共晶转变温度约为420 ℃; 合金在凝固过程中首先析出α-Mg树枝晶, 固液界面前沿铝含量不断增多, 富铝的残余液体在枝晶间隙发生共晶转变, 最后凝固形成α-Mg和β-Mg17Al12的共晶组织; 由于该共晶组织含量少, 共晶α-Mg往往依附初生相α-Mg形核生长, 并将β-Mg17Al12相推向α-Mg枝晶的晶界, 形成离异共晶组织。

The phase transition temperature points of AZ81 magnesium alloy were measured by differential thermal analysis experiments, and the microstructure at phase transition points was obtained through liquid quenching method. The solidification behavior and microstructure evolution were analysed by optical microscopy, scanning electron microscopy and energy disperse spectroscopy. The results show that the solid-liquid phase transition temperature and eutectic transition temperature of AZ81 magnesium alloy were about 590 ℃ and 420 ℃, respectively. During the solidification of AZ81 magnesium alloy, α-Mg dendrites would precipitate firstly, aluminum content increased at the forefront of solid-liquid interface, eutectic transformation of Al-rich residual liquid occured at dendrite clearance, and finally solidified to eutectic microstructure of α-Mg and β-Mg17Al12. Moreover, as the eutectic microstructure was few, nucleation and growth of eutectic α-Mg phase were often dependent on α-Mg primary phase, and divorced eutectic microstructure formed through pushing β-Mg17Al12dendrite to the grain boundary of α-Mg.