Microstructure and mechanical properties of friction stir processed Cu with an ideal ultrafine-grained structure

Ultrafine-grained (UFG) Cu with uniform microstructure was successfully prepared by friction stir processing (FSP) under additional water cooling. FSP Cu exhibited equiaxed grains with low dislocation density, weak texture, and high fraction of high-angle grain boundaries. Isotropy and tension-compression symmetry were achieved in FSP Cu sample, which provided an ideal model material to investigate the intrinsic mechanical behavior of the UFG material. Enhanced strain hardening was achieved in FSP Cu due to the special microstructure which was effective in accumulating dislocations, resulting in good strength-ductility synergy. This study provides a feasible strategy of preparing bulk UFG materials with good mechanical properties.