Influence of Melt Mass and Pouring Height on the Microstructure of an Al–Si Alloy Prepared by Controlled Diffusion Solidification with Simultaneous Mixing

In this study, pure Al and Al–12Si alloy were used as precursor alloy 1 and precursor alloy 2 respectively to prepare the target alloy of Al–8Si by controlled diffusion solidification with simultaneous mixing, and the effects of melt mass and pouring height on the casting microstructures were investigated via simulation and experiment. The results from the simulation indicates that as the melt mass increased, both temperature and concentration fields became more uniform, i.e., the mixing effect was improved due to the increased melt momentum. But when the melt mass exceeded 2 kg, an opposite effect was achieved because of the increased friction in the melt. With the increase in pouring height, the mixing effect was continuously enhanced due to the steadily increased momentum. However, more gas bubbles were entrapped within the melt. A better mixing effect means that more and finer pure Al pockets were formed and more uniformly distributed in the Al–12Si matrix melt. Thereby more α-Al grains nucleated to form a structure with finer and more spheroidal grains. Subsequent experiment results indirectly confirmed these simulation results. A casting with a grain size of 45.7 μm and shape factor of 1.36 was obtained at melt mass of 2 kg and pouring height of 600 mm.