Mixing process and nucleation of an Al-Si alloy during controlled diffusion solidification with simultaneous mixing and effect of mixing rate

A controlled diffusion solidification (CDS) process with simultaneous mixing of two precursor melts was proposed in this work. The mixing process and the effect of mixing rate were simulated taking Al-8 wt% Si alloy as a model material, and the nucleation and growth mode were then discussed based on the simulation results. Finally, experiments were conducted to confirm the simulation results and the feasibility of this process. The results indicated that blending effectively operated after the two-stream mixture entered into the bottom mixture due to the generated intensive convection or vortex, resulting in formation of numerous small pockets of the two melts. Copious nucleation then promptly occurred in the pure Al pockets that were rapidly supercooled by surrounding Al-12Si pockets, and the alpha-Al nuclei then grew in a stable solid/liquid interface mode that was resulted from the unique distribution characteristic of Si element in the melt ahead of the interface. As a result, a microstructure with small nondendritic or spheroidal grains was achieved. The blending result was continuously improved as mixing rate increased, which was confirmed by the experiment result, both the average size and shape factor of primary alpha-Al grains in the CDS castings decreased with increasing mixing rate, and these two parameters at the employed highest rate of 1.6 kg/s were about 52 mu m and 1.35, respectively. The proposed CDS can completely overcome the shortcomings of the traditional one, and is a more promising way for casting components or preparing ideal nondendritic semisolid slurry or ingot for semisolid forming.

Automated summary

In this study, a controlled diffusion solidification (CDS) process with simultaneous mixing of two precursor melts was proposed. The effects of mixing rate on the microstructure were studied through simulation and experiments. The results showed that increasing the mixing rate can improve the blending result and achieve a microstructure with small nondendritic or spheroidal grains.