Effect of Cooling Rate on the Microstructure and Solidification Characteristics of Al–20%Mg 2 Si In Situ Composites Using Computer-Aided Thermal Analysis Technique

The formation, size and morphology of Mg 2 Si intermetallics as the reinforcement particles in Al–Mg 2 Si in situ composites have important effects on the mechanical properties of the alloy. Solidification conditions, particularly cooling rate, have a direct effect on the microstructure and characteristics of the reinforcement particles. In this research, the effect of different cooling rates on the microstructure and solidification parameters of Al–20%Mg 2 Si in situ composite has been investigated using cooling curve thermal analysis technique. For this purpose, the thermal analysis curves of this composite have been plotted at five different cooling rates. The results demonstrated that the variation of cooling rate affects the characteristic temperatures of primary Mg 2 Si phase and the eutectic reactions. By increasing the cooling rate from 0.4 to 17.1°C/s, the nucleation temperature of primary Mg 2 Si, binary eutectic and ternary eutectic is increased, while growth temperature of both eutectic reactions is decreased. Also, Mg 2 Si reinforcement particles changed from coarse dendritic to fine polygonal shape accompanied with decrease in size and increase in density.