Bi对AZ80镁合金凝固行为及显微组织的影响

EFFECTS OF Bi ADDITION ON SOLIDIFICATION BEHAVIOR AND MICROSTRUCTURE OF AZ80 MAGNESIUM ALLOY

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-Mg_(17)Al_(12)和Mg_3Bi_2相组成,其中Mg_3Bi_2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-Mg_(17)Al_(12)(437℃)被三元共晶转变L→α-Mg+β-Mg_(17)Al_(12)+Mg_3Bi_2(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 primaryα-Mg matrix,divorced eutecticβ-Mg_（17）Al_（12） phase and Mg_3Bi_2 phase.The Mg_3Bi_2 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-Mg_（17）Al_（12）＋Mg_3Bi_2（at 435℃） takes place during solidification of AZ80-2%Bi alloy instead of the binary eutectic transformation L→α-Mg＋β-Mg_（17）Al_（12）（at 437℃） in AZ80 alloy.Comparing with AZ80 alloy,the nucleating temperature of primaryα-Mg in AZ80- 2%Bi alloy is decreased from 568.8℃to 562.6℃,and the eutectic temperature is also decreased from 424.2℃to 421.1℃.