Microstructure and Mechanical Properties of Ultrafine Quaternary Al-Cu-Si-Mg Eutectic Alloy

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 & DEG;C upon heating, suggesting a eutectic reaction. The cast alloy microstructure consisted of four phases, alpha-Al, Al2Cu (theta), 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 alpha-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 & PLUSMN; 35 MPa, a fracture strength of ~1 GPa and a compressive fracture strain of 4.7 & PLUSMN; 1.1%. The high strength is attributed to a combination of a refined eutectic structure and strengthening from multiple hard phases.