Microstructural Evolution and Distributions of Grain Boundary in SPD Processed Al–3 mass%Mg Alloy

Abstract

SPD-processed Al alloys have an ultra-fine-grained microstructure and extremely high strength. The strength of SPD-processed Al alloy exceeds the estimated it by the grain size using Hall-Petch relationship. SPD-processed Al has high dislocation density because the excess introduced strain remains in dynamically recrystallized grains. The excess dislocation may form the low angle grain boundary during dynamic recrystallization. Al-Mg alloy represents especially large strengthening by dislocation hardening after SPD not only smaller grain size than pure Al. This is because the stacking fault energy (SFE) of the alloy is lowered by Mg solute atom. The dislocation movement become suppressed during DRX in low SFE alloys. As a result, SPD-processed Al-Mg alloys have extremely fine-grained (~0.25 µm) microstructure. SFE of the alloy may also affect the formation of low angle grain boundary and dislocation accumulation in the grain interior. The dislocation distributions could result the degree of extra-hardening. The distributions of dislocation and low angle grain boundary in ECAE processed Al-3 mass%Mg alloy were investigated by EBSD and XRD techniques. Annealing after ECAE for recovery the strain provides the relaxation of the strain hardening, in spite of the LAGB fraction remains static.