Papers by Author: Hans Erik Ekström

Abstract: The microstructural evolution during annealing of a commercial Al-Mn alloy cold rolled to a high strain was investigated using EBSD and Gallium Enhanced Microscopy. The precipitation of manganese, coarsening of precipitates and tensile properties were monitored at different stages. It was found that during recovery the subgrains grow until they reach the limiting subgrain size when the driving force has been reduced to the same level as the Zener drag from the dispersoids. New grains are nucleated at constituent particles and a few are able to grow. The softening during recovery and the onset of discontinuous recrystallisation are analyzed and discussed in terms of recent theories of recovery and recrystallisation.

Abstract: The softening behaviour during annealing was investigated in cold and hot rolled AA3103 alloys after different heat treatments. It was found that the evolution of boundary spacing determined using gallium enhanced microscopy gives a very good representation of the softening behaviour. The results show that cold rolled Al-Mn alloys soften by continuous growth of the subgrain structure, “continuous recrystallisation”, provided the pre-treatment of the ingots has been made to avoid too high a density of dispersoids and the cold rolling reduction has been very large. The very high strain creates a microstructure with a large fraction of high angle boundaries that are mostly parallel to the sheet surface. A recently developed subgrain growth model which takes the effect of solute drag into account, gives a good description of the softening kinetics. The solute drag is controlled by bulk diffusion of Mn. The simultaneous precipitation of Mn from the solid solution takes place by grain boundary diffusion of the Mn atoms mainly to pre-existing particles. The solute concentration decreases as the inverse of the boundary spacing, which is due to the grain growth mainly in the thickness (normal) direction.