Investigation of the Portevin-LeChâtelier effect in Al-3wt.%Mg alloys by strain-rate and stress-rate controlled tensile tests

The development of Portevin-LeChâtelier (PLC) deformation bands and their propagation are studied by laser scanning extensometry during room temperature deformation of a polycrystalline Al-3wt.%Mg alloy. Tensile tests with imposed constant strain-rates are compared with imposed constant stress-rates. The jerkily propagating PLC type B bands as observed in strain-rate control, disappear in stress control, where a single or multiple bands propagate very rapidly along small distances. This is different from type A behavior with continuous soliton-like propagation along the specimen axis. The characteristic quantities, like shear concentration within the band, propagation rates, and width of the bands are measured and compared for the two testing modes, with the aim to gain insight into the mechanism controlling band propagation. The propagation modes are well described by a recent PLC model which includes dynamic strain aging kinetics of dislocations and the dynamics of plastic deformation by dislocation motion and strain hardening.