Revealing the effect of Si content on the microstructure and properties of Al–Si alloy by experiments and phase-field simulation

The grain size of aluminum alloy is closely related to solute content and solidification conditions. This study investigated the influence of Si content on the solidification microstructure and properties of the Al-Si binary alloy by experiments and phase field simulation. The experimental results indicated that the microstructure of Al-Si alloy changes from coarse columnar grains to uniformly distributed equiaxed grains as Si content increases from 0 to 7 wt.%, and the average grain size of Al-2Si is the smallest (2.2 mm). Meanwhile, the tensile strength of Al-Si alloys increases from 56.9 MPa to 111 MPa with increasing Si content, whereas the ductility decreases from 30% to 2.5%. Moreover, high casting temperature will produce coarse columnar crystals, low casting temperature forms equiaxed crystals, the optimal casting temperature in this study is 30 oC above the liquidus. Phase field simulations reveal that the evolution of Al-Si microstructures is governed by two dimensionless parameters: the initial temperature (T0), related to casting temperature and solidification interval, and the latent heat (K1), connected to latent heat, specific heat, and solidification interval. For a certain alloy composition (Al-2Si), the grain size exhibits a non-monotonic trend, decreasing initially and then increasing as T0 increases, with an optimal T0 value of 1.42. When the Si content varies between 2 to 7 wt.%, the average grain sizes decrease as K1 increases, with the maximum K1 value observed at 1.38 for Al-2Si.