Mechanical properties of Al–15Mg₂Si composites prepared under different solidification cooling rates

The effect of different cooling rates (2.7, 5.5, 17.1, and 57.5°C/s) on the solidification parameters, microstructure, and mechanical properties of Al−15Mg₂Si composites was studied. The results showed that a high cooling rate refined the Mg₂Si particles and changed their morphology to more compacted forms with less microcracking tendency. The average radius and fraction of primary Mg₂Si particles decreased from 20 µm and 13.5% to about 10 µm and 7.3%, respectively, as the cooling rate increased from 2.7 to 57.5°C/s. Increasing the cooling rate also improved the distribution of microconstituents and decreased the grain size and volume fraction of micropores. The mechanical properties results revealed that augmenting the cooling rate from 2.7 to about 57.5°C/s increased the hardness and quality index by 25% and 245%, respectively. The high cooling rate also changed the fracture mechanism from a brittle-dominated mode to a high-energy ductile mode comprising extensive dimpled zones.