Effect of grain size on tensile behaviour of a submicron grained Al–3 wt-%Mg alloy produced by severe deformation

Abstract

Equal channel angular extrusion has been used to deform an Al–3 wt-%Mg alloy to an effective strain of 10, resulting in a 0.2 µm grain size. In the as deformed condition the yield strength was increased to ∼500 MPa. During annealing the grain structure coarsened uniformly and the yield stress was found to follow the Hall–Petch relationship, even in the submicron range. There was an abrupt transition in elongation at a grain size of ∼0.5 µm. Samples with smaller grain sizes showed no uniform elongation and limited ductility. For slightly greater grain sizes there was only a relatively small reduction in elongation, compared to a coarse grained material, while the yield stress was still increased by a factor of over four. Reducing the grain size to the submicron range led to far higher Lüders strains than are normally observed in Al–Mg alloys.