The effect of stacking fault energy on equilibrium grain size and tensile properties of nanostructured copper and copper–aluminum alloys processed by equal channel angular pressing

Pure copper and copper–aluminum alloys (aluminum content of 2.3 at%, 7.2 at%, and 11.6 at% with stacking fault energies (SFEs) of about 48 mJ/m2, 21 mJ/m2, and 8 mJ/m2, respectively) were processed by equal channel angular pressing (ECAP) at room temperature for 8 passes to generate a nanoscale grain size. The effect of SFE on microstructure refinement and tensile properties of these materials were investigated. Microstructural observations indicated that the grain size of as-ECAPed alloy decreased monotonically with increasing Al concentration, i.e. with decreasing SFE. A very low SFE was especially favorable for achieving a true nanocrystalline structure (e.g. d≈57 nm in Cu–11.6 at% Al) by twinning and shear banding. The tensile strength and uniform elongation of nanostructured copper–aluminum alloys were simultaneously enhanced owing to the significant grain size refinement, solid solution strengthening and enhanced strain hardening capability.