中文摘要：

采用垂直向下的高梯度定向凝固装置，研究了有热溶质对流的Al-38．5％Cu（质量分数，下同）过共晶合金中定向凝固组织变化。结果表明：热溶质对流造成界面前沿的溶质成分（Cu元素）沿轴向减少。在定向凝固速率为5μm／s，合金溶质成分减少到37％Cu以下时，合金定向凝固组织中，初生θ-Al2Cu相会消失，组织变为全耦合生长的共晶组织。合金凝固的固相分数（fs）≥0．49时，组织变为全耦合生长共晶组织所对应的溶质成分的理论计算结果与实验结果相吻合。

英文摘要：

Thermosolutal convection has a remarkable effect on solidified microstructure. The microsttuctures of directionally solidified Al-38.5%Cu hypereutectic alloy were investigated by using the apparatus with a high temperature gradient. The results show that the solute composition ahead of the solid/liquid interface （copper element） decreases along the solidification direction due to the thermosolutal convection in the melt. The theoretical calculation results indicate that the primary θ-Al2Cu phase of faceted dendrites disappears when the alloy composition decreases to 37%Cu for a pulling velocity of 5μm/s, in agreement with the experimental results. The microstructure of directionally solidification is eutectic structure of entirely coupled growth without any faceted dendrites of primary θ-Al2Cu when the solid fraction reaches 0.49 and the alloy composition is less than 37%Cu.