Modelling the microstructural evolution during annealing of a severely deformed A1-3% Mg alloy

The microstructural development during annealing of an Al 3%Mg alloy, after severe deformation, has been studied (and compared to predictions of Monte-Carlo simulations and a 2D vertex network model). The alloy was deformed by ECAE at 20degreesC to a total effective strain of ten, without rotation of the billet. This produced a highly directional deformation structure, comprised predominantly of thin ribbon grains with an average width of similar to 100 nm and aspect ratio of similar to 10. The ribbon grains were cross-linked by transverse low angle boundaries (LAGBs), producing a 'ladder', or 'bamboo' like, structure. On annealing no signs of discontinuous recrystallisation were observed. However, the deformation structure was found to rapidly evolve into a uniform submicron equiaxed grain structure, by the break up of the ribbon grains during the early stages of grain growth. The vertex network simulation showed close agreement to the experimental observations and demonstrated that the grain break up resulted from necking caused by the surface tension of the lower mobility transverse LAGBs.