Microstructure and mechanical properties of ultrafine quaternary al‐cu‐si‐mg eutectic alloy

Abstract

The microstructure evolution and mechanical properties of quaternary Al‐Cu‐Si‐Mg eutectic alloy prepared via arc melting and suction casting were studied. This alloy exhibits a single endothermic DSC peak with a melting temperature of 509 °C upon heating, suggesting a eutectic reaction. The cast alloy microstructure consisted of four phases, α‐Al, Al2Cu (θ), Si and Al4Cu2Mg8Si7 (Q), in the eutectic cells and also in the nano‐scale anomalous eutectic in the intercellular regions. The eutectic cells show different morphologies in different parts of the sample. Well‐defined orientation relationships between the α‐Al, Al2Cu, and Q phases were found in the eutectic cell centres, while decoupled growth of Q phase occurred at the cell boundaries. The bimodal microstructure exhibits excellent compressive mechanical properties, including a yield strength of 835 ± 35 MPa, a fracture strength of ~1 GPa and a compressive fracture strain of 4.7 ± 1.1%. The high strength is attributed to a combination of a refined eutectic structure and strengthening from multiple hard phases.