Microstructure of severely deformed Al-3Mg and its evolution during annealing

The submicron microstructure developed here after heavy deformation of Al-3Mg by equal channel angular pressing (ECAP) is shown to consist of an elongated grain and cell structure of width 70-80nm and 300-400nm length. There is also a high dislocation density inside these grains with some tendency to dislocation arrangement as a cell structure. Many of the grain boundaries are shown to be of low-medium angle and are not the randomly misoriented, high-angle boundaries generally assumed to be present. Annealing at low temperatures leads to a reduction of dislocation density, some reduction of grain length as transverse boundaries form in the elongated grains, and grain coarsening. At higher temperatures a duplex structure forms as some regions show localized recrystallization. The relationship of grain boundary misorientation and high-temperature coarsening and recrystallization to the applied heavy strain and alloy composition is discussed. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.