Using novel strain aging kinetics models to determine the effect of solution temperature on critical strain of Al-Zn-Mg-Cu alloy

In this study, the critical strain of Al–5.28Zn–2.66Mg–1.52Cu (wt.%) alloy, related to the Portevin-Le Chatelier (PLC) effect, was investigated using a series of uniaxial tensile tests after solution treatment at various temperatures. The experimental results show that critical strain first decreases (namely, the “inverse” behavior) and then increases (namely, the “normal” behavior) as strain rate increases, for each solution treatment case and the corresponding inflection point for transition between “inverse” and “normal” behavior moves from right to left on the critical strain-strain rate curves for an increase in the solution temperature. In view of the existing theoretical PLC models that cannot accurately describe this complex behavior, a set of dynamic strain aging kinetics models was developed based on the relationships between, strain rate, temperature, critical strain and critical strain rate. Several temperature-dependent variables have been considered, and it is shown that “inverse” to “normal” transition can be well explained by a newly proposed competition mechanism between dislocation stress and dynamic strain aging stress. During “inverse” to “normal” transition, both concentration of solute atoms and distance between the obstacles at which solute atoms cluster, play a key role. Moreover, the relationship between temperature and solute atom concentration, revealed by the transmission electronical microscopy (TEM) and differential scanning calorimetry (DSC) test results, verifies the proposed models.