Accumulation of deformation and acoustic emission in aluminum-magnesium alloy AMg6 in the conditions of deformation of the structural transition

In the course of thermomechanical loading of an aluminium-magnesium alloy under soft loading conditions, a monotonic-stepwise or quasi-stepwise character of deformation accumulation has been observed. Monotonous accumulation of deformation is followed by a monotonous growth of the root-mean-square voltage of acoustic emission, as well as deformation jumps are followed by high-amplitude discrete signals of acoustic emission. The accumulation of deformation in an aluminum-magnesium alloy in a non-isothermic cycle is characterized by the two-stage process: low-temperature monotonous, with a low rate of deformation accumulation, and high-temperature stepwise or quasi-stepwise with a high-rate of deformation accumulation. The temperature transition point from the low-temperature area to the high-temperature area has the value of approximately 570°C and determines a low-to-high-rate transition of deformation accumulation. This kind of transition from the low-temperature area of deformation accumulation to the high-temperature one is characterized by a change in the mechanism of deformation accumulation and represents a deformation structural transition. Thus, the deformation structural transition is the transition from deformation accumulation that is controlled by thermally-activated dislocations climb to deformation accumulation that is controlled by grain boundary processes of perfect (lattice) dislocations generation at triple boundary junctions and occurs when mechanical stress, temperature and acoustic emission energy achieve certain critical values. While the mechanical stress grows, the transition temperature goes down and the acoustic emission oscillation energy rises thus showing that a certain balance of critical parameters is kept. The deformation structural transition is the result of the joint action of thermal fluctuations, static shifts of stress field and dynamic shifts of standing acoustic waves formed by primary signals of the acoustic emission at natural resonators of the sample volume under deformation.