Response of partitioning to cooling rate for different solutes in aluminum alloys

Abstract

It is commonly recognized that the cooling rate has a substantial effect on solute partitioning and its resultant microsegregation during solidification. The classical dendrite tip undercooling theory clarifies the mitigation of microsegregation by increasing the cooling rate. However, most of the studies focused on binary alloys, leaving an open question as to whether the microsegregation of different solutes in a multi-component alloy system exhibits a relieving degree similar to increasing cooling rate. Taking a widely used 6022-type Al alloy (Al-0.76Mg-0.93Si-0.2Fe) as a model alloy, the current study reveals that the microsegregation of Mg gets alleviated to the greatest extent, followed by those of Si and Fe when the cooling rate increases from 5 to 128 K/s. This phenomenon is attributed to the solute-based difference in response to partitioning to cooling rate (denoted as Rk). We propose a theoretical equation to quantify Rk, and the Rk values of solute Mg, Si, and Fe successfully explain the rank of solute partitioning in experiments. Furthermore, a broad range of Rk values of other commonly used alloying elements in Al alloys were calculated and ranked, delivering a handy tool to predict the microsegregation behavior and solubility of different solute elements upon sub-rapid solidification, which is consistent with experimental observation. This framework can also be extended to other multi-component alloy systems.