Effect of solid solution treatment on microstructure and mechanical properties of Al–Si–Cu–Mg alloy prepared by semi-solid squeeze casting

In order to explore the solid solution strengthening mechanism of Al-Si series alloy under semi-solid squeezing casting an experiment was conducted to cast, heat treat, and then characterize the material. OM, SEM, and TEM were selected as tools to characterize the microstructure and mechanical properties of semi-solid extrusion Al–Si–Cu–Mg alloy under different solution times. The results show that the eutectic Si phase fuses, the Al 2 Cu phase rapidly dissolves into the matrix, and the dislocation density in the matrix slightly decreases at the initial stage of solution. When the solution time reaches 8 h, the spheroidization degree of the eutectic Si phase reaches its optimum shape as measured by aspect ratio and size. The Al 2 Cu phase is essentially completely dissolved into the matrix, leading to a significant reduction in the dislocation density within the matrix. The alloy reached a relatively high mechanical properties after 1 hour of solid solution at 525 °C. The dissolution of the Cu element in the matrix and the enrichment of dislocation lines around the Si phase together contribute to strengthening the α-Al phase. Additionally, another strength peak emerges at 8 h of solid solution. The second strength peak is mainly attributed to the refinement of the eutectic Si phase and the solution strengthening of the Al 2 Cu phase.