Evolution of microstructure and texture in commercial pure aluminum subjected to high pressure torsion processing

Abstract

Commercially pure aluminum was chosen as a model face-centered cubic material for a detailed investigation of microstructural and textural evolution during processing by high pressure torsion. Severe grain refinement was observed as the average grain size decreased from ~ 85 μm to ~ 1.22 μm at an equivalent strain of ɛ = 99. It is observed that at early stages of deformation an accumulation of dislocations inside grains occurs. More straining results in an increase of misorientation and eventually gives rise to fragmentation of parent grains to new smaller grains. A near saturation of grain refinement is observed after a strain of ɛ = 15. Kernel average misorienation maps suggest the occurrence of a weak recovery process at relatively large strains, resulting in annihilation of dislocations inside the grains. The texture results show that a simple shear type texture develops during deformation, although it is a relatively weak texture due to the nature of simple shear strain mode and the occurrence of grain fragmentation. The full constraint Taylor model and the viscoplastic self-consistent crystal plasticity model were employed to reproduce the experimental textures at relatively large strains. It is shown that the Taylor model leads to a better agreement between simulated and experimental data. It is observed that a satisfactory simulation of the texture evolution at severe strain amplitudes cannot be obtained with models that ignore the effect of grain fragmentation.