Extra-Hardening of SPD-Processed Al-Mg Alloy with Minimum Grain Sizes

Abstract

Severe plastic deformation (SPD) processing of Al alloys could obtain high strength by grain refinement mechanism. The minimum grain size of Al alloy, obtained at higher strain rate at low temperature, is determined the stacking fault energy of the alloy. SPD-processed pure Al metal, has high stacking fault energy, has relatively large grain size. During SPD processing, large strain is introduced, and the dislocation is rearranged in the specimen. The re-arrangement of dislocation in SPD-processed Al alloy with intermediate stacking fault energy significantly delayed, thus the strain remains in the grain interior. The extra-hardening, a kind of strain hardening, results from an incomplete of dynamic recrystallization during SPD processing. Al-Mg solid solution alloy has intermediate stacking fault energy and the minimum grain size of this alloy approaches about 200 nm after SPD. The mechanical property of this alloy is remarkably higher than the predictable strength by Hall-Petch relationship due to the extra-hardening. In addition, the increase in strength by the extra-hardening varies with the Mg content of Al-Mg alloy. In this study, the effect of Mg content, i.e. the stacking fault energy of the alloy, on the degree of the extra-hardening of SPD-processed Al-Mg alloy was investigated in terms of the dislocation density and low-angle grain boundary of the alloy.