Annealing response of binary Al-7Mg alloy deformed by equal channel angular pressing

The annealing response in a binary Al-7Mg alloy processed at room temperature by equal channel angular pressing (ECAP) has been investigated via X-ray diffraction (XRD), electron-probe micro analysis (EPMA) and electron backscattering diffraction (EBSD). After ECAP and subsequent annealing, Mg remains mainly homogeneously distributed in solid solution. A bimodal structure with ultrafine grains accompanied by micrometer-sized crystallites was developed after 3 passes. Upon annealing at ~275 °C for 96 h, extensive recovery was observed in the as-deformed material, leading to a relatively uniform microstructure; at ~300 °C a discontinuous recrystallization initiated in less than 30 s with subsequent grain growth clearly evident. Such remarkable thermal stability, i.e., slower recovery and recrystallization kinetics, of the present material, in contrast to other severely deformed commercial pure Al and Al-Mg alloys, is due mainly to the presence of high Mg solid solution contents, the formation of the bimodal structure consisting of both coarse crystallites and ultrafine grains. In addition, the possible Mg-containing precipitates during annealing might also retard the recrystallization kinetics.