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Keywords:Al-Mg alloy Electron backscattering diffraction (EBSD) Severe plastic deformation (SPD) Grain refinement Microstructure Grain boundaries a b s t r a c tStrain induced grain refinement of an Al-1 wt.%Mg alloy processed by equal channel angular pressing (ECAP) at cryogenic temperature is investigated quantitatively. The results show that both mean grain and subgrain sizes are reduced gradually with increasing ECAP pass. ECAP at cryogenic temperature increases the rate of grain refinement by promoting the fraction of high angle grain boundaries (HAGBs) and misorientation at each pass. The fraction of HAGBs and the misorientation of Al-1 wt.% Mg alloy during ECAP at cryogenic temperature increase continuously as a function of equivalent strain. Both {110} and {111} twins at ultrafine-grained size are observed firstly in Al-Mg alloy during ECAP. The analysis of grain boundaries and misorientation gradients demonstrates the grain refinement mechanism of continuous dynamic recrystallization.

The potential for significant grain refinement in pure aluminium (99.9%) processed by means of equal channel angular pressing at 523 K (T/Tm ∼ 0.6) has been demonstrated. The mean grain size was significantly reduced from 1.2 mm to 4 µm after eight passes. The stored energy and high-angle grain boundary fraction increase until 6 passes and then remain almost constant until 8 passes. The grain refinement occurred in two stages, initially driven by the evolution of deformation inhomogeneties (deformation bands, microbands) and then through recovery and the interaction of deformation inhomogeneties into fine grains.

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