Low-stabilty states of aluminum crystal lattice and acoustic emission under high-temperature straining

Using aluminum as an example it is experimentally established that strain accumulation under low-stability condition at the temperatures higher than 0.5 melting temperature exhibits a non-monotonic behavior and represents sharp deformation changes within a wide range of scale levels (including macroscale). The effects of this stepwise deformation are accompanied by high-amplitude acoustic emission signals. An analysis of the anomalous metal behavior and acoustic emission shows that the activation volume of an elementary deformation event under this low-stability state is exponentially increased with the deformation temperature, indicating an increased scale of cooperative atomic displacements and manifestation of low stability of the crystal lattice of this atomic configuration. The macroscopic character of this stepwise deformation provides evidence on a correlation between elementary deformation events within a volume larger than one strain band. It is assumed that the amplitude of an acoustic signal can serve a criterion of this correlation.