Zn-Cu包晶合金定向凝固组织演化 Ⅰ.实验现象及分析

MICROSTRUCTURE EVOLUTION IN UNIDIRECTION- ALLY SOLIDIFIED Zn-Cu PERITECTIC ALLOY I. Experiment and Analysis

对亚包晶、过包晶以及接近包晶点成分的Zn-Cu二元合金进行了定向凝固实验,研究其在45 K/mm的温度梯度以及2—6400 μm/s凝固速度下的组织选择及演化规律,发现Zn-2％Cu的低速凝固组织为η相单相生长,高速下为η相胞晶+胞晶间ε相的组织; Zn-2.7％Cu,Zn-3％Cu以及Zn-4％Cu的低速凝固组织为η相基体+ε相定向枝晶,高速凝固组织为η相胞晶+ε相等轴晶.基于最高界面生长温度判据,在充分形核假设下对凝固过程中的相选择规律进行了分析,并与实验结果较好的吻合.

Zn-Cu alloys with hyperperitectic, hypoperitectic and near peritectic point compositions were unidirectionally solidified under temperature gradient of 45 K/mm and with growth rate range from 2 μm/s to 6400 μm/s. It is found that the typical structure for Zn-2%Cu is composed by single phase η under low solidification velocity and 77 cellular with intercellular e phase under higher solidification velocity, and the typical structure for samples with higher Cu composition is aligned e dendritic in matrix of 77 under lower solidification velocity and η cellular with e equiaxied dendritic under higher solidification velocity. Phase selection of the solidified samples was calculated based on the criterion of the highest interface growth temperature with the assumption of abundant nucle-ation conditions, and the reasonable accordance between the calculated and experimental results was achieved.