Mechanical Properties of Thixoformed Al–Si–Cu Alloys

This study aims to evaluate the microstructure and mechanical behavior of Al–Si–Cu alloys (Al–wt%Si–2.5wt%Cu, Al–5wt%Si–2.5wt%Cu, and Al–7wt%Si–2.5wt%Cu) thixoforged through controlled partial melting. The alloys were subjected to temperatures that ensured a solid fraction of 45% and held for varying durations of 0, 30, 90, and 210 s. They were then immediately thixoforged in two different types of equipment: eccentric and a pneumatic press. The thermal treatments promote globularization of the primary-phase particles, with globules measuring around 70 µm. Tensile testing was carried out to characterize the mechanical behavior, and the results were equivalent or superior to those obtained for the as-cast structures. The thixoforged alloys were also subjected to T4 heat treatment with a solution treatment temperature of 540 °C for 10 h. Better distribution of the Si eutectic and a reduction in the size of the Si particles compared with the as-cast conditions were achieved. T4 treatment resulted in a significant improvement in mechanical properties, especially for the Al7Si2.5Cu alloy thixoforged in a pneumatic press, for which the yield strength reached 200 MPa, the ultimate tensile strength 292 MPa and the elongation 7.6%. Results indicate the feasibility of using these alloys to produce metal parts by thixoforging, especially when a pneumatic press is used.