强制对流对 Al-4.5wt%Cu 合金枝晶生长的影响

研究了ACRT（坩埚加速旋转技术）对Al-4.5wt%Cu合金在静态温度梯度GL为120℃/cm时枝晶生长的影响。实验发现，在给定抽拉速度下，枝晶一次间距λ1随着坩埚旋转强度的增大而减小；而在给定的坩埚旋转参数下，λ1随着抽拉速度的增大而降低。经过线性回归，发现λ1∝V-b,此处V为生长速度；b的取值范围为0.31～0.38,并随着坩埚旋转强度的增大而减小。此外，坩埚加速旋转产生的强制对流限制了枝晶高次分枝的生长，促使一次枝晶生长过程中的分叉。通过对强制对流的具体分析，解释了ACRT对枝晶生长影响的机理。

INFLUENCE OF CONSTRAINED CONVECTION ON THE DIRECTIONAL DENDRITE GROWTH OF Al 4 5% Cu ALLOY

The influence of ACRT (accelerated crucible rotation technique) on the directional dendrite growth of Al 4 5wt%Cu binary alloy has been investigated at the still temperature gradient of 120℃/cm. It was found that for the same growth rate, the primary dendrite arm spacing, λ 1, decreased with increasing maximum crucible rotation rates and associated acceleration, while for the same crucible rotation parameters, λ 1 reduced with increasing growth rates. Several linear regressions showed that λ 1 ∝ V -b , where V was the growth rate; b was a constant decreasing with increasing maximum crucible rotation rates, and ranging from 0 31 to 0 38. Furthermore, the constrained convection produced by ACRT restrained the growth of secondary dendrite arms, and promoted the branching off and twisting of primary dendrites. The mechanisms of the influences of ACRT on directional dendrite growth were suggested based on the detailed analysis of the constraind convection. It was the Ekman flow with high speeds that enhanced the heat and mass transportation ahead of the S/L interface and produced an obvious asymmetrical distribution of solute around a dendrite tip.