Effect of Standing Time after Mixing on the Mixture Microstructure of an Al-Si Alloy during Controlled Diffusion Solidification with Simultaneous Mixing

Abstract

Taking pure Al (938.15 K) and Al-12Si (858.15 K) melts as two precursors and the Al-8Si alloy as the target alloy, the effect of the standing time after mixing on the microstructure of a mixture during controlled diffusion solidification with simultaneous mixing was investigated via a simulation and experiment. The simulation results indicate that the entrapped air will promptly form bubbles and cause the mixture to overflow within a short time of 1.2 s. An effective blending action still occurs during the initial stage (i.e., 0–0.5 s) of the standing process, resulting in the significant homogenization of the temperature field due to the thermal conductivity being much higher than the solute diffusivity. This is due to the large difference between the two thermophysical parameters, causing nuclei to rapidly form in the pure Al melt close to the interface of the pure Al/Al-12Si melts during mixing. Some of the nuclei will remelt, and others will only grow towards the pure Al melt side in a stable solid/liquid interface during standing, resulting in nondendritic Al grains and an increase in their size but a decrease in their number. These changing tendencies of grain morphology, size and number due to the standing time are consistent with those from the experiment, implying the employed simulation and calculation, as well as the achieved results, are reasonable and reliable.

Keywords

• controlled diffusion solidification
• nucleation
• growth mode
• nondendritic microstructure