Effect of fine-grained structural Al–12%Si materials on morphologies and crystal defects of eutectic Si in HCC Al–12%Si alloy billets

Abstract: The microstructure of horizontal continuous casting Al–12%Si alloy billets was optimized by fine-grained structural materials of the same composition as the master alloy. The effect of fine-grained structural materials on the morphologies and crystal defects of eutectic Si was studied by SEM, TEM and HRTEM. The results show that the secondary dendrite arm spacing of α-Al decreases and the morphologies of eutectic Si change from coarse needle-like to fine fibrous shape with 30% master alloy addition. Furthermore, the nature and distribution of the defects inside Si crystals are quite different as before. Two oblique crossing sets of twins present in the modified eutectic Si. In addition, the TEM and HRTEM results reveal that the growth mechanism of eutectic Si transforms from step growth to twin plane re-entrant growth mechanism due to the addition of fine-grained structural materials. [Copyright &y& Elsevier]