Effect of the Strain and Strain Rate on Microstructure Evolution and Superplastic Deformation Mechanisms

Parameters of superplasticity of the Al–7.6% Mg–0.6% Mn–0.25% Cr alloy have been studied in the range of 490–520°C, and the optimum temperature of deformation has been determined. The evolution of the grain structure in the bulk and on the surface of samples during the superplastic deformation at a temperature of 510°C has been analyzed. The contribution of grain-boundary sliding has been estimated in the strain-rate regime of superplastic deformation according to the results of the analysis of changes in the structure of the surface with preliminarily applied marker scratches. The contribution of grain-boundary sliding to the total deformation is 20–30%; the contribution of diffusion creep decreases from 40 to 20% with an increase in the deformation rate by an order of magnitude, from 1 × 10–3 to 1 × 10–2 s–1. The intragranular deformation is localized in the peripheral regions of grains and in the region of striated zones.