Kinematics of formation and cessation of type B deformation bands during the Portevin-Le Chatelier effect in an AlMg alloy

Using digital image correlation technique, various stages of development of localized deformation bands caused by the Portevin-Le Chatelier (PLC) instability of plastic flow are examined at strain rates corresponding to abrupt stress drops akin to relaxation oscillations. Diffuse deformation bands are found prior to stress drops. Although the respective increase in the local strain rate is relatively weak, it is immediately observed over the entire region of the nascent PLC band. Moreover, diffuse bands are also detected at the beginning of reloading after the end of stress drops, thereby indicating that the termination of plastic instability proceeds through a progressive depletion of the strain localization. Weak transient strain localizations that do not develop into a PLC band are also observed during reloading.