定向凝固铝铜合金一次枝晶间距的研究

RESEARCH ON THE PRIMARY ARM SPACING IN UNIDIRECTIONLLY SOLIDIFIED AL-CU ALLOY

本文实验研究了凝固参数对铝铜合金一次枝晶间距的影响。结果表明,一次枝晶间距Z_1,并不随生长速度V或温度梯度G的增加而连续减小,而是在V=(1-3)V_(CS)/k时达到极大值,在G=kG_(CS)时急剧改变,其中V_(CS)和G_(CS)是平面生长成分过冷极限下的生长速度及温度梯度。仅在高速生长条件下,关系式Z_1=KG^-(1/2)V-(1/4)才成立,K——与合金性质有关的常数。一次间距的极大值或突变对应于胞晶——枝晶转变。一次枝晶是在“生长——淹没——竞争再生长”的过程中生长的,竞争再生长的方式是“扰动再生长”及“新晶再生长”。

Jn this paper, the effect of solidification parameters on the primary arm spacing of Al-Cu alloy has been studied experimentally. The results show that the primary arm spacing does not continuously decrease with the increase in growth velocity or temperature gradient, but goes through a maximum or a catastrophe as a function of growth rate V or temperature gradient G, at V = (l-3)Vcs/k or G =kGcs, where Vcs and Gcs are the critical velocity and temperature gradient at the limit of constitutional undercooling. Only for the high velocity regime do we find the relationship Z = KG-2V-b to hold true, where K depends on the alloy composition. The maximum or the catastrophe of the primary arm spacing is correlated with cell-to-dendrite transition. The primary dendrite grows in such a process as “growing-engul fed-competitively growing”. The major way of competitive growth is “engulfed-new crystal growing” and “engulfed-disturbance growing”.