Al-4%Cu合金定向凝固枝晶/胞晶转变速率的研究

Research of Dendrite/Cellular Interfacial Transitional Velocity in Directionally Solidified Al-4%Cu Alloy

通过实验和理论对比研究Al-4%(质量分数)Cu合金定向凝固胞晶/枝晶转变过程,得到胞晶/枝晶转变发生在尖端半径变化的拐点处。采用KGT模型与非平衡效应研究与胞晶/枝晶转变过程相对应的高速枝晶/胞晶转变特征。结果表明:尖端半径和界面温度均随抽拉速率的增加而减小,到达临界值后又急速增大。枝晶/胞晶转变发生在尖端半径和界面温度的拐点处,即在尖端半径和界面温度最小时发生转变;溶质截留在枝晶/胞晶转变过程中作用明显,大大减小了微观偏析。

The transition from cellular to dendrite was obtained at the spindle of tip radius by comparing experimental and theoretical study on Al-4% Cu alloy during directional solidification. It was found that the tip radius fell quickly in cellular stage but fell slowly in dendrite stage. The KGT （W. Kurz, B. Giovanola and R. Trivedi） model and non-equilibrium effect were applied to research the tip radius and interface temperature in order to obtain the transitional characteristic from dendrite to cellular. The results indicated that the tip radius and interface temperature were both decreased with increasing withdrawal rate, after reached the critical points, finally turned to rise sharply. It was eventually obtained that the transition from dendrite to cellular was occurred at the spindle of tip radius and temperature, that was the tip radius and tip temperature reached minimum, VRmin and VTmin. Moreover, solute trapping became obvious during the transition, which led to decrease of microsegregation.