Microstructural evolution of dilute Al–Mg alloys during processing by equal channel angular pressing and during subsequent annealing

Equal channel angular pressing (ECAP) is a materials processing method that allows very high strains to be imposed, leading to extreme work hardening and microstructural refinement, with minimal change of external sample dimensions. It offers possibilities of good mechanical properties, such as high strength and ductility, while allowing flexibility of choice of alloy composition for better corrosion behaviour, lower materials costs, and so on. The microstructure of an Al–3 wt.% Mg alloy is examined after processing by ECAP as well as its evolution during subsequent heat treatments for precipitation, recrystallization, or grain coarsening. Fine microstructures are produced by deformation which coarsen steadily on annealing. The nature of the grain boundaries after deformation and after annealing, as well as the grain sizes obtained, is reported. It is interesting to consider to what extent such heavy-deformation processing offers the possibility to achieve extremely fine grain sizes (towards the nano-scale) by the control of alloy composition, deformation conditions, and subsequent heat treatments.