Microstructure evolution and mechanical properties of Al-8wt. % Si semi-solid billet fabricated by powder metallurgy liquid phase reaction sintering

The Al-8wt. % Si semi-solid billets were successfully prepared by a new liquid phase reaction sintering process with Al and Si elemental powders. The reaction mechanism of the Al and Si elemental powders was investigated, and the thermodynamics and dynamics of the reaction process were studied. The effect of the microstructure evolution on the mechanical properties was analyzed. In the reaction process, the reaction product Al(Si)_(L) liquid phase wets the Al particles well, and the liquid phase content increased with increasing reaction temperature and time. It was found that the kinetic model given by ψ = 4.6 × 10⁵exp(-1.05 × 10⁵/RT)t^1/3 can accurately predict the actual liquid phase formation fraction. With increasing reaction temperature, the viscosity of the liquid phase decreases and the Si atom diffusion coefficient increases. This will increase the formation rate of the liquid phase and decrease the length of lath Si. The increased liquid phase content increases the strength of the billet and decreases its elongation. The shear crack is the main reason for the instability of the billets during the deformation process. Acting as a crack source, Si particles accelerate the generation and propagation of cracks, and promote the instability fracture of the billet.