Plastic deformation of micrograined magnesium alloy AZ31 at low temperatures

The features of the plastic deformation of a micrograined magnesium alloy AZ31 under tension in the temperature range 4.2-295 K were studied. The samples were deformed in two structural states: the initial (after eight passes of equal channel angular pressing, 8ECAP) and annealed (after isothermal annealing at 573 K) states. In both cases, with decreasing temperature, an increase in the yield strength, strain hardening coefficient, and a decrease in ductility were observed. The dependence of the hardening coefficient of the deformation is nonmonotonic compared to the initial one, which is explained by an increase in twinning activity due to an increase in grain size upon annealing. The low Hall-Petch parameters for the yield strength at room temperature indicate a high activity of the basal slip of the dislocations, due to the mixed texture that forms after 8ECAP and does not change radically upon annealing. The yield strength of the studied polycrystals is determined by the thermofluctuation motion of mainly basal dislocations. The empirical parameters of this motion in the temperature range 4.2-295 K, obtained from the analysis of the temperature dependences of the yield strength and activation volume, correspond to the mechanism of interaction of dislocations with local obstacles formed by impurity atoms and forest dislocations.