The evolution of homogeneity and grain refinement during equal-channel angular pressing: A model for grain refinement in ECAP

Samples of pure aluminum and an Al-6061 alloy were subjected to equal-channel angular pressing (ECAP) for up to eight passes at room temperature. The Vickers microhardness was recorded on the polished cross-sections of each as-pressed billet and the results are plotted in the form of color-coded maps to provide a pictorial depiction of the hardness distributions throughout the cross-sections. The results show the hardness increases by a factor of ∼2 in the first pass through the die but thereafter there is only a minor increase. The microhardness distribution is homogeneous in the unpressed condition but becomes inhomogeneous after a single pass and then reasonably homogeneous in subsequent passes. The results reveal some differences between the behavior of pure Al and the Al-6061 alloy. These results and microscopic observations are used to develop a model for the process of grain refinement during ECAP.