采用恒速及跃迁减速定向凝固方法制备了Al-40%Cu (质量分数)过共晶合金, 对金属间化合物初生Al₂Cu相的组织及取向演化进行了研究. 结果表明, 当定向凝固速率恒定为10 μm/s, 抽拉100 mm时, 合金成分随着凝固距离的增大而减小, 初生Al₂Cu相枝晶由规则棱面V型转变为非棱面形貌, 在抽拉距离80 mm附近消失, 其生长方向由[110]方向转变为(121)晶面的法线方向; 当定向凝固速率由10 μm/s跃迁减速至2 μm/s时, 合金成分在变速界面后随着凝固距离的增大先增大后减少, 初生Al₂Cu相枝晶由规则棱面V型变为非棱面长条状形貌而后消失, 其体积分数先增大后减少, Al₂Cu相的生长方向由[110]方向转变为平行于热流方向的[001]方向. 定向凝固恒速与跃迁变速下初生Al₂Cu相枝晶生长机制存在异同, 凝固工艺参数成为影响枝晶最终组织形态和生长方向的主要因素.

Dendrite is a fundamental growth pattern in alloy solidification. Normally, dendrites with a specific growth orientation which can remarkably influence casting properties have attracted many great interests. The previous investigations mainly focus on the growth of simple monophase dendrites solid solution. For complex intermetallics in solidification, the correlation between processing parameters and microstructure morphologies with the preferred growth directions has not been shed a light. In this work, considering intermetallic Al₂Cu phase has crystalline anisotropy and can exhibit colorfully complicated growth morphologies with specific growth direction in different solidification conditions, the primary Al₂Cu phase growth behavior of Al-40%Cu (mass fraction) hypereutectic alloy was investigated by using a high thermal gradient directional solidification apparatus. The Al₂Cu phase growth behavior in the experiments included its change in growth morphology and orientation transition. With solidification distance increasing, due to the alloy liquid composition ahead of the solid/liquid interface approaching the eutectic point, the primary Al₂Cu dendrite transited from regular faceted V-shaped morphology to the entirely coupled eutectic at 10 μm/s. Its growth direction changed from [110] direction to the normal direction of (121) plane. The EBSD result indicated that the [001] direction of Al₂Cu phase was along the direction of heat flux. As the growth rate was changed abruptly from 10 to 2 μm/s, the alloy liquid composition ahead of the solid/liquid interface increased firstly and then decreased to the eutectic point. It caused that the primary Al₂Cu dendrite transited from regular faceted V-shaped morphology to long smooth lath morphology, and finally disappeared to form the entirely coupled eutectic. Moreover, the growth direction of Al₂Cu phase changed from [110] direction to [001] direction. The experimental results show that the directional solidification process parameter is the dominant factor affecting the final morphology and growth direction of dendrites.