富铈混合稀土对Al-80%Si合金凝固行为和组织的影响

Effects of cerium-rich mischmetal on solidification behavior and microstructure of Al-80%Si alloy

采用高速摄影仪和扫描电子显微镜研究富铈混合稀土(RE)加入量对Al-80%Si(质量分数)合金悬浮试样凝固行为和凝固组织的影响规律。结果表明:Al-80%Si合金中初生硅的生长特性、晶粒尺寸和分布受过冷度影响明显;随着RE加入量的增加,Al-80%Si合金中初生硅由小平面生长向中间生长方式转变所需的临界过冷度ΔT1以及由中间生长向非小平面生长方式转变所需的临界过冷度ΔT2均越来越低;当RE加入量达到1.5%(质量分数)时,ΔT1和ΔT2分别降至最低值78和180 K;继续增加RE的加入量,ΔT1和ΔT2不发生变化。在同一临界过冷度ΔT2下,随RE加入量的增加,初生硅的尺寸从40μm减小到20μm。

The effect of the addition level of cerium-rich mischmetal（RE） elements on the solidification behavior and as-solidified microstructure for the Al-80%Si（mass fraction, %） alloy prepared by electromagnetic levitation method was investigated by using high speed camera and scanning electron microscope. The results show the growth behavior, grain size and distribution of primary silicon are obviously dependent on the nucleation undercooling. The critical undercooling ΔT1, for the growth-mode transition from lateral mode to intermediary one, and the critical undercooling ΔT2, for the growth-mode transition from intermediary mode to continuous one, both decrease with increasing the RE addition level. When the RE content is 1.5%（mass fraction, %）, the values of ΔT1 and ΔT2 reach the minimum of 78 K and 180 K, respectively. With further increasing the RE content, the critical undercoolings, ΔT1 and ΔT2 then tend to be steady. Under the same critical undercooling ΔT2, the size of primary silicon decreases from 40μm to 20μm with the increase of RE content.