High strength and toughness squeeze casting AlSi9MnMgCu alloy for automotive lightweighting

AlSi10MnMg alloy is widely used in automotive die casting structure, yet the synergistic improvement of strength and toughness is still a core challenge for the application of this alloy. To address this issue, a novel high-strength and toughness AlSi9MnMgCu alloy was designed and fabricated via squeeze casting. The effects of T6 heat treatment on their microstructure and mechanical properties were investigated. The as-cast alloy consists of an α-Al matrix, eutectic Si phase, and three intermetallic compounds as α-Al 15 (Fe,Mn) 3 Si 2 , θ-Al 2 Cu, and Q-Al 5 Cu 2 Mg 8 Si 6 . It exhibited a tensile strength of 253 MPa, a yield strength of 137 MPa, and an elongation of 8.5%. After T6 heat treatment with solution at 530 °C for 3 h followed by aging at 180 °C for 4 h, the alloy achieved superior comprehensive mechanical properties with a tensile strength of 340 MPa, a yield strength of 255 MPa, and an elongation of 9.8%. TEM characterization revealed that the as-cast interwoven network-like Si phase fragmented gradually after solution treatment with discontinuous grain boundaries forming. Subsequent peak aging induced precipitation of abundant strengthening phases including short rod-like Q' and path-like θ'. The fragmentation of the network-like coarse Si phase, precipitation strengthening, and grain refinement synergistically enhanced both the strength and ductility of the AlSi9MnMgCu alloy.