The process of grain refinement in equal-channel angular pressing

Experiments were conducted on high purity aluminum to investigate the process of grain refinement during equal-channel angular (ECA) pressing. Samples were subjected to 1 to 4 pressings and then sectioned for microstructural examination in three mutually perpendicular directions. The results show that a single pressing leads to the development of subgrain bands. The subsequent microstructural development in additional pressings depends upon whether these repetitive pressings are conducted with no rotation of the sample (route A), with a rotation of 90° between each pressing (route B) or with a rotation of 180° between each pressing (route C). The subgrains evolve more rapidly into arrays of high angle boundaries using route B, less rapidly using route C and the evolution is slowest using route A. The results are explained by considering the shearing patterns developed in the samples during each processing route.