Investigation of the influences of ternary Mg addition on the solidification microstructure and mechanical properties of as-cast Al–10Si alloys.

A hypoeutectic Al–10Si-2.0 Mg ternary alloy with high strength and high ductility was developed for as-cast service conditions. The effects of eutectic-forming element Mg on the primary α-Al dendrites, eutectic Si structure, Mg 2 Si intermetallic compound, mechanical properties and fracture behavior were systematically investigated via multiscale characterization methods. Interestingly, the results demonstrated that with the increasing Mg content, the secondary dendrite arm spacings of the primary α-Al dendrites were significantly reduced, and the grain size was refined, while the flaky eutectic Si structure was fully modified into a coral-like morphology. Additionally, the size of the Mg 2 Si intermetallic phase sharply decreased, and it was distributed much more uniformly in the interdendritic/intergranular eutectic regions. In contrast with the binary Al–10Si alloy, the yield strength, the ultimate tensile strength and the fracture strain were substantially enhanced to 159.4 MPa, 275.3 MPa and 14.1%, respectively, which correspond to improvements of 131.0%, 70.4% and 27.0%, respectively. The underlying mechanisms that were responsible for the evolution of the microstructure and mechanical properties are explicitly discussed. • Grain size and SDAS were substantially refined by growth restriction effect of Mg. • Eutectic Si phase and Mg2Si intermetallic were highly modified with increasing Mg. • Strength and ductility were increased simultaneously and achieved best at 2.0% Mg. [ABSTRACT FROM AUTHOR]