Evolution of the microstructure that is formed in a coarse-grained commercial Al-6% Mg-0.4% Mn-0.3% Sc alloy upon equal-channel angular pressing (ECAP) in the temperature range from 200 to 450°C (∼0.5–0.8T _m) has been studied. The samples were deformed through route A up to a true strain ɛ ∼ 12 and quenched in water after every ECAP pass. A fine-grained structure with an average grain size from 0.4 to 2.5 μm was formed upon high degrees of deformation in the temperature range from 200 to 450°C. In contrast to the low- and middle-alloy aluminum alloys, an increase in the ECAP temperature led to a continuous increase in the volume fraction of newly formed fine grains from 0.62 at 200°C to 0.85 at 450°C. At a temperature of 300°C, there was observed a violation of the monotonic dependences of the size and volume fraction of new grains on the deformation temperature as a result of the formation of a bimodal structure with the size of fine grains of about 1 μm and the size of coarse grains of about 8 μm. The latter were formed as a result of intensive development of static recrystallization during spontaneous annealing of samples in the matrix channel during ECAP and/or interoperational heating. The development of a microstructure upon intermediate temperatures is discussed in terms of the formation of a large potential for grain boundary migration created by a high mobility of grain boundaries upon high temperatures and increased driving force for recrystallization as a result of intense suppression of dynamic recovery in a hard-to-deform aluminum alloy.