Ultrafine-grained structure development and deformation behavior of aluminium processed by constrained groove pressing

The severe plastic deformation method known as constrained groove pressing was used to produce ultrafine-grained microstructure in recrystallized aluminium (99.99%) at room temperature. The impact of repeated groove pressing, upon microstructure refinement was investigated by transmission electron microscopy of thin foils. Changes in mechanical properties measured by tensile and by hardness tests were related to microstructure development. The formation of banded subgrain microstructure with dislocation cells, and appearance of polygonal subgrains was a common feature observed in deformed plate subjected to the first pass. The substantial impact of strain upon strength increase was observed after the first pressings. The yield stress and ultimate tensile strength reached a maximum after four passes. A loss of ductility was observed in all processed plates. Hardness values measured in different areas of the deformed plates indicated heterogeneous strain distribution even after large degrees of straining.