Influence of high temperature retrogression and re-aging treatments on microstructures and properties of 7150 alloy

In this paper, the influence of a novel heat treatment process, namely high temperature retrogression and re-aging treatment (HTRRA) on properties and microstructures of 7150 aluminum alloy was investigated by optical microscope, field emission scanning electron microscopy, microhardness and thermodynamic calculation. The experimental results show that the alloy retrogressed at 425°C for 30 minutes and re-aging exhibits hardness up to 178HV with retention of an electric conductivity of 35.5%IACS. The decrease in hardness and increase in electric conductivity, comparing with the alloy in T6 temper, are associated with the formation of S (Al ₂CuMg) grain interior phase and θ (Al ₂Cu) phase in grain boundary. Furthermore, the HTRRA treatment shows slow sensitivity to retrogression time due to thermal stability of S phase, which might be applied to thick section components of ultra-high strength aluminum alloys.