Solidification Characteristics of Ex situ Particulate-Reinforced Aluminum Matrix Composites

This work aimed to elucidate and compare the solidification characteristics of A356.2, A356.2/5% SiC, A356.2/5% Al2O3, and A356.2/5% ZrO2 metal composites with and without adding Bi element by using the Fourier thermal analysis method. Microstructural and XRD analysis showed that reinforcement particles have been successfully embedded in the A356.2 alloy through the compo-casting route. Thermal analysis results show that the cooling rate of the A356.2 matrix alloy, as measured in the experimental set-up, was 0.8 °C/s and increased to 1.9 °C/s in the composites. The nucleation temperature of α-Al increased slightly (0.6 °C), and undercooling (8.9–11 °C) was observed for all composites. The nucleation temperature of the Mg2Si phase and solidus temperature of composites were lower than the A356.2. Moreover, the growth temperature and recalescence magnitude of eutectic Al-Si did not change remarkably. The solidification temperature range and solidification rate increased by 5% and 33%; however, the solidification time decreased by 21%. The solid fraction at the coherency point increased, which is associated with an expansion in the time difference between nucleation and the coherency point. However, adding Bi resulted in the depression of eutectic growth temperature and the refinement of eutectic Si. These data infer that the solidification kinetic of A356.2 and their composites are identical. It cannot be concluded that reinforcement particle acts as nucleation agents for both α-Al and eutectic Si.