Grain Floatation During Equiaxed Solidification of an Al-Cu Alloy in a Side-Cooled Cavity: Part II—Numerical Studies

Abstract

In this article, a single-phase, one-domain macroscopic model is developed for studying binary alloy solidification with moving equiaxed solid phase, along with the associated transport phenomena. In this model, issues such as thermosolutal convection, motion of solid phase relative to liquid and viscosity variations of the solid-liquid mixture with solid fraction in the mobile zone are taken into account. Using the model, the associated transport phenomena during solidification of Al-Cu alloys in a rectangular cavity are predicted. The results for temperature variation, segregation patterns, and eutectic fraction distribution are compared with data from in-house experiments. The model predictions compare well with the experimental results. To highlight the influence of solid phase movement on convection and final macrosegregation, the results of the current model are also compared with those obtained from the conventional solidification model with stationary solid phase. By including the independent movement of the solid phase into the fluid transport model, better predictions of macrosegregation, microstructure, and even shrinkage locations were obtained. Mechanical property prediction models based on microstructure will benefit from the improved accuracy of this model.

Effect of Super-gravity Field on Grain Refinement and Tensile Properties of Cu–Sn Alloys

“…Wu's simulation study did not take account of the movement of equiaxed grains, which can markedly influence the solidification structure of castings. 22,23) Also, the solidification structure refinement of Al-Cu alloys in super-gravity field has been investigated systematically in our recent study, 24) which demonstrated that the "crystal rain" caused by super-gravity contributed to the grain refinement.…”

The Refining Mechanism of Super Gravity on the Solidification Structure of Al-Cu Alloys

“…When super gravity is applied throughout the solidification process, the crystals collect in the middle of the sample, shown in Figure 7d. In a normal gravity field, the crystals also settle [25,35,36]. In our experimental result shown in Figure 7e, the solidification structure at the bottom area is obviously finer than that at the top of the sample, a difference caused by the settling of the crystals.…”

“…Hence the crystals cause the FGZ at the bottom of the sample, as shown in Figure 7 b. With further treatment, ending when the solid fraction reaches 80 wt %, the crystals reverse direction and began to move upward within the sample, gathering in the middle of the sample as shown in Figure 7 c. When super gravity is applied throughout the solidification process, the crystals collect in the middle of the sample, shown in Figure 7 d. In a normal gravity field, the crystals also settle [ 25 , 35 , 36 ]. In our experimental result shown in Figure 7 e, the solidification structure at the bottom area is obviously finer than that at the top of the sample, a difference caused by the settling of the crystals.…”

Model order reduction of solidification problems

“…Figure 1: The mushy zone is a mixture of solid and liquid that leads to a reduced fluid flow (adapted from [6]).…”