采用加热-激冷方法和OM, SEM, XRD, DSC等分析手段, 研究了AZ80-Bi镁合金的凝固行为, 分析了合金的凝固组织特征及其演变过程, 阐明了合金的凝固序列. AZ80-2%Bi(质量分数)合金的铸态显微组织由α-Mg, β-Mg17Al12和Mg3Bi2相组成, 其中Mg3Bi2相以片状和颗粒状两种形态存在. 将2%Bi加入AZ80合金后, 影响了合金的凝固序列, 二元共晶转变L→α-Mg+β-Mg17Al12 (437 ℃)被三元共晶转变L→α-Mg+β-Mg17Al12+Mg3Bi2 (435 ℃)代替. 2%Bi的加入使AZ80合金的初晶形核温度由568.8 ℃降低至562.6 ℃, 共晶平台温度由424.2 ℃降到421.1 ℃.
The solidification behavior and as--cast microstructure in AZ80-Bi magnesium alloy were analysed by OM, SEM, XRD and DSC. Meanwhile, the evolution of the solidification microstructure of AZ80-2%Bi alloy was studied by heating-quenching experiments. The results show that the as-cast microstructure of AZ80-2%Bi consists of primary α-Mg matrix, divorced eutectic β-Mg17Al12 phase and Mg3Bi2 phase. The Mg3Bi2 phase exists in the flake-like and granule-like morphologies. With 2.0%Bi addition, the solidification procedure of AZ80 magnesium alloy is changed. The ternary eutectic transformation L→α-Mg+β-Mg17Al12+Mg3Bi2 (at 435 ℃) takes place during solidification of AZ80-2%Bi alloy instead of the binary eutectic transformation L→α-Mg+β-Mg17Al12 (at 437 ℃) in AZ80 alloy. Comparing with AZ80 alloy, the nucleating temperature of primary $\alpha$--Mg in AZ80--2\%Bi alloy is decreased from 568.8 ℃ to 562.6 ℃, and the eutectic temperature is also decreased from\linebreak 424.2 ℃ to 421.1 ℃.
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