Characterization and modeling of the hardening and softening behaviors for 7XXX aluminum alloy subjected to welding thermal cycle

The evolution of thermo-elasto-plastic stress-strain during welding process plays a key role in determining the welding residual stresses and mechanical properties of welded joints for age-hardening 7XXX aluminum alloy, which is influenced by the softening and hardening behaviors. In this study, a Gleeble 3800 thermo-mechanical testing machine was employed to simulate the welding thermal cycle process of 7XXX aluminum alloy, and dynamic yield strengths under different temperatures were measured to elucidate the softening behavior. An isothermal multi-level cyclic loading tests at various temperatures were conducted to characterize the cyclic hardening feature. The calculation formulas for the proportion of kinematic and isotropic hardening model were deduced, and the cyclic hardening behavior was quantitatively described. A softening model and a nonlinear mixed hardening model were explored to simulate the evolution of dynamic yield strength and the cyclic hardening behavior, and excellent agreements were obtained between predicted and measured dynamic yield strengths and cyclic stress-strain curves.