Critical dynamics of localized instabilities of plastic flow in the Al-Mg alloy

The critical dynamics of the spatial-temporal fluctuations related to the stress of the plastic flow (Portevin-Le Chatelier effect) of inclined cylindrical samples made of Al-Mg (AMG6) alloy was investigated at strain rates 0.4-1.7·10-1 s. Such samples’ shape allows achieving large deformations (up to 80 %) without destruction. The plastic flow of the investigated alloy exhibits multiscale features of strain localization along the entire length of the plastic flow curve. The first critical value is determined by the appearance of the multiple regions of localized plasticity, with signs of autosoliton dynamics exhibiting the correlated behavior at the macroscopic size of the sample. The two values of "critical" strains corresponding to the range of stochastic dynamics were determined which is characteristic for non-equilibrium critical systems. The transition through the second critical value is associated with qualitative changes of collective modes in ensembles of defects: a transition from autosoliton modes providing the plastic strain localization to collective “blow-up” modes responsible for damage-failure transition. The localization of plastic flow was studied by the structural analysis of the morphology of the surface using the optical interferometer-profilometer NewView-5010 for the subsequent calculation of the scale invariant (Hurst index) and the spatial scale of the region on which there is a correlated behavior of microshears. It was shown that the plastic flow instability and the fully developed turbulent flow in liquids reveal universality features of momentum transfer, that could be linked to the same “universality classes”.