Creep aging behavior and performance of Al-Zn-Mg-Cu alloys under different parameters in retrogression aging treatment

A study was conducted to better understand how different parameters, namely, regression aging time and regression aging temperature, affect the creep aging properties, i.e., the creep deformation and performance of Al-Zn-Mg-Cu alloy during regressive reaging. The corresponding creep strain and mechanical properties of samples were studied by conducting creep tests and uniaxial tensile tests. The electrical conductivity was measured using an eddy-current conductivity meter. The microstructures were observed by transmission electron microscopy (TEM). With the increase in regression aging time, the steady creep strain first increased and then decreased, and reached the maximum at 45 min. The steady creep strain increased with the increase in regression aging temperature, and reached the maximum at 200 °C. The level of steady creep strain was determined by precipitation and dislocation recovery. Creep aging strengthens 7B50-RRA treated with regression aging time at 190 °C for 10 min, and the difference in the mechanical properties of alloy becomes smaller. The diffusion of solute atoms reduces the scattering of electrons, leading to a significant improvement in electrical conductivity and stress corrosion cracking (SCC) resistance after creep aging. The findings of this study could help in the application of creep aging forming (CAF) technology in Al-Zn-Mg-Cu alloy under RRA treatment.