Thermal deformation behavior and processing maps of 7075 aluminum alloy sheet based on isothermal uniaxial tensile tests

Abstract

Process parameters and their effects on thermal-mechanical properties of aluminum alloys are vitally important for the successful manufacture of aluminum alloy panel components under hot forming condition. In this study, firstly, thermal-mechanical properties of 7075 aluminum alloy sheets under hot forming conditions were comprehensively investigated using a series of isothermal uniaxial tensile tests at different temperatures and strain rates on a Gleeble 3500 thermal mechanical simulator. Based on the experimental results, the temperature rise ΔT generated from plastic deformation was further calculated considering the fraction of plastic work converted into heat, β, and the fraction of deformation heat appearing as a temperature rise, δ. ΔT increases with an increase in strain rate and a decrease in deformation temperature, with a maximum temperature rise ΔTmax reaching 33.5 K. Furthermore, taking ΔT into consideration, the relationship model between the work hardening rate, temperature and strain rate was constructed according to the Zener-Hollmon parameter. The variation of the work hardening rate with strain rate and temperature can be interpreted using this model. Finally, to determine the optimal processing parameters, the processing maps of 7075 aluminum alloy were established subsequently under the experimental conditions. The optimal processing parameters for 7075 aluminum alloy are located within the windows: (1) temperature, 573–680 K and strain rate, 0.368–8.1 s−1; (2) temperature, 695–723 K and strain rate, 0.05–1 s−1. According to the microstructure observations, it can be concluded that the main softening mechanism of “safe” domains is dynamic recovery (DRV) and the continuous dynamic recrystallization (DRX) can be effectively retarded due to the presence of precipitated particles. The work performed in this research, for the first time, provides quantitative evaluations of process parameters on the hot deformation of aluminum alloy sheet forming using processing maps considering corresponding microstructural evolutions, which enables to provide useful guides for process designers of sheet metal forming.