Improvement of mechanical properties of Al–Si–Cu alloy diecastings combined with Cd microalloying and semisolid forming

Al–Si–Cu alloy with and without 0.2 wt% Cd was prepared using traditional and semisolid diecasting. The microstructure, porosity, and mechanical properties of the four alloys in as-cast and T6 heat-treated states were systematically studied and compared. The mechanism of microstructure refinement and property strengthening of semisolid diecasting Al–Si–Cu alloy containing Cd was analyzed. During T6 heat treatment, Cd-rich particles precipitated first and acted as a nucleating agent for θ′-Al2Cu nanoparticles. This resulted in a smaller size and the greater density of the θ′-Al2Cu precipitated phase containing the Cd alloy. Semisolid diecasting Cd microalloyed Al–Si–Cu alloy had excellent mechanical properties under T6 heat treatment. Its ultimate tensile strength, yield strength, elongation, and hardness were 447 MPa, 313 MPa, 6.7%, and 150 HV, respectively. Compared with traditional diecasting Al–Si–Cu alloy without Cd, the above properties were increased by 36%, 57%, 81% and 15%, respectively. This finding was due to the densification, refinement, and homogenization of the microstructure brought about by semisolid formation, as well as the precipitation and strengthening of θ′-Al2Cu nanoparticles with fine and high density due to Cd microalloying. •Improvement of mechanical properties of Al–Si–Cu alloy combined with Cd microalloying and semisolid diecasting.•Cd microalloyed Al–Si–Cu alloy diecastings had θ′-Al2Cu particles with fine and high density in T6 state.•The UTS, YS and EL of semisolid diecasting Cd microalloyed Al–Si–Cu alloy were 447 MPa, 313 MPa, and 6.7%, respectively.•This study clarifies the heterogeneous nucleation effect of pre-precipitated Cd-rich particles on θ′-Al2Cu.•Discussion on the mechanism of microstructure refinement and property strengthening of semisolid diecasting Al–Si–Cu–Cd alloy.