Comparative Study of Microstructure and Properties of Hypoeutectic Al-Si Alloys Being Cast With and Without Melt Thermal Treatment

This study investigated the microstructure and mechanical properties of several hypoeutectic Al-xSi (x = 0, 1, 3, 5, 7, 9) alloys prepared with and without melt thermal treatment. The overall study showed a trend of effective utilization of grain refiner until the transition point (3 wt.% Si) and the slope of graph between grain size vs. wt.% of Si remain similar for the samples prepared with or without chemical refinement. This also indicates that the role of Si in decreasing grain size is more dominating than the poisoning of Ti above transition point. Melt thermal-treated alloys exhibited less significant changes in grain size, especially below the transition point, but significant changes in their mechanical properties. The melt thermal treatment also causes partial refinement of eutectic Si particles by which the coarse silicon particles are broken up into smaller pieces and this has neither been observed in unrefined alloys nor refined alloys.