Abstract:

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.

Key words: constrained convection, ACRT, dendrite growth, dendrite twisting