A unified physically-based model describing complex unloading behavior in cold and hot deformation process of aluminum alloys

During the cold and hot deformation of metals, the nonlinearity in unloading is mainly caused by dislocationassociated behaviors and creates challenges for the prediction of springback law and residual stress distribution after springback. In this paper, a unified physically-based model for describing the dislocation density evolution in unloading after cold and hot deformation was proposed firstly by considering the combined effects of reverse slip of reversible mobile dislocations (under back stress and the static recovery) and recrystallization (after deformation) on the dislocation density evolution in unloading. Furthermore, an anelastic strain model associated with dislocation behaviors was established for predicting the microplastic strain in unloading after cold and hot deformation by considering the effects of strain-induced dislocation multiplication and the dislocation annihilation/consumption caused by dynamic recovery and dynamic recrystallization on the reversible mobile dislocation density evolution during deformation. The established dislocation density evolution model and anelastic strain model were evaluated using the experimental results obtained from the hot compression of homogenous aluminum alloys and the cold compression of extruded aluminum alloys. The results indicated that the established models are able to accurately predict nonlinear unloading behavior and nonlinearly varying microplastic strain. Meanwhile, it was also found that, for cold deformation, the reverse slip of reversible mobile dislocations driven by back stress is the leading reason for the nonlinearity of unloading, and the strain hardening and recovery during deformation are main factors affecting the anelasticity of unloading; for hot deformation, the reverse dislocation slip, static recovery and recrystallization collectively affect the nonlinearity in unloading, and the anelasticity is affected not only by strain hardening and dynamic recovery but also by dynamic recrystallization during loading process.