Correlation versus randomization of jerky flow in an AlMgScZr alloy using acoustic emission

Jerky flow in solids results from collective dynamics of dislocations which gives rise to serrated deformation curves and a complex evolution of the strain heterogeneity. A rich example of this phenomenon is the Portevin-Le Chatelier effect in alloys. The corresponding spatiotemporal patterns showed some universal features which provided a basis for a well-known phenomenological classification. Recent studies revealed peculiar features in both the stress serration sequences and the kinematics of deformation bands in Al-based alloys containing fine microstructure elements, such as nanosize precipitates and/or submicron grains. In the present work, jerky flow of an AlMgScZr alloy is studied using statistical analysis of stress serrations and the accompanying acoustic emission. As in the case of coarse-grained binary AlMg alloys, the amplitude distributions of acoustic events obey a power-law scaling which is usually considered as evidence of avalanchelike dynamics. However, the scaling exponents display specific dependences on the strain and strain rate for the investigated materials. The observed effects bear evidence to a competition between the phenomena of synchronization and randomization of dislocation avalanches, which may shed light on the mechanisms leading to a high variety of jerky flow patterns observed in applied alloys.