Observation of Portevin-le Chatelier effect in aluminum alloy 7075-w under a heterogeneous stress field

The kinetics of Portevin-Le Chatelier (PLC) bands in the hole-expansion of a circular hole using a flat-headed punch are investigated for a solid-solution heat-treated AA7075 aluminum sheet. This experiment is performed under quasi-static strain-rate and at room temperature. The full strain field in the hole periphery during the entire deformation is measured by a stereo-type digital image correlation system. The observations of PLC band activity are based on the thickness strain-rate field. Each individual PLC band appears aligning along the radial direction, spanning diverse stress states, and propagates along the circumferential direction during the life time from nucleation to dissipation. Furthermore, the nucleation sites of all the PLC bands are recorded during the experiment, which shows that the nucleation frequency of a PLC band is influenced by the plastic anisotropy, and that it increases proportionally to the level of thickness strain.