Effect of heat treatment on the microstructure and mechanical properties of extruded Al-4Cu-1Li-0.4Mg-0.4Ag-0.18Zr Alloy

This study was undertaken to evaluate the effect of heat treatment on the microstructure and mechanical properties of extruded Al-4Cu-1Li-0.4Mg-0.4Ag-0.18Zr alloy. After a three-step homogeneous treatment (480 °C/12 h + 500 °C/12 h + 540 °C/2 h), a Cu-containing secondary phase was found to be dissolved in the α-Al matrix and distributed along the grain boundary in the as-cast state. The effect of the aging temperature, aging time, and amount of pre-deformation on the mechanical properties at ambient temperature was investigated. The results showed that higher aging temperature and longer aging time resulted in higher yield strength (YS), ultimate tensile strength (UTS), and lower elongation (EL). The increase in the amount of pre-deformation significantly promoted YS of the studied alloy, at the cost of a minor decrease in EL. Among the tested samples, the one stretched by 4.5% and aged at 125 °C for 32 h exhibited the highest yield strength. Good mechanical properties, characterized by YS = 629 MPa, UTS = 663 MPa and EL = 9.2% were obtained at ambient temperature. The precipitation behavior and strengthening mechanism were also investigated. The variations in size, number density, and distribution of the T1 (Al2CuLi) and θ′ (Al2Cu) phases under different treatment conditions were the main reason for the change in mechanical properties.