Si对ZA84镁合金凝固过程中三元化合物相选择的影响

摘要

借助X射线衍射仪、扫描电镜和差示扫描量热仪等分析手段研究了Si对金属型铸造ZA84 (Mg-8Zn-4Al-0.3Mn)镁合金中τ(Mg32(Al, Zn)49)和φ(Al2Mg5Zn2)两相之间的相选择影响.结果表明,随着ZA84合金中Si加入量的增加,合金的液相线温度下降,并且凝固区间减小.ZA84合金中的三元金属间化合物主要是τ相,φ相只占少量.当在ZA84合金中加入一定量的元素Si时,三元金属间化合物的优先析出次序发生改变,φ相优先析出而τ相被抑制.对相选择现象进行凝固动力学分析表明,在过冷熔体中存在临界过冷度,τ相与φ相析出时若熔体的过冷度大于此临界值,则τ相优先析出而φ相受到抑制,否则,φ相优先析出而τ相被抑制.%Effect of silicon on the phase selection between τ phase (Mg32(Al, Zn)49) and φ phase (Al2Mg5Zn2) in ZA84 (Mg-8Zn-4Al-0.3Mn) magnesium alloy produced by steel mold cast was studied using X-ray diffractometer, scanning electron microscope and differential scanning calorimeter. The results show that with increasing Si addition in ZA84 alloy, the liquidus temperatures of the alloys and the solidification temperature ranges decrease. The ternary compound in ZA84 alloy is mainly τ phase and a little φ phase. When adding Si to ZA84 alloy, the preferential precipitation sequence of the ternary compounds changes, φ phase preferentially forms, whereas τ phase is suppressed. The solidification kinetics study of phase selection indicates that there is a critical degree of undercooling of the melt. If the undercooling exceeds the critical degree, τ phase preferentially forms while φ phase is suppressed; otherwise, φ phase preferentially forms while τ phase is suppressed.