Effect of stacking fault energy on microstructural feature and back stress hardening in Cu-Al alloys subjected to surface mechanical attrition treatment

Three Cu-Al alloys with nominal Al contents of 2.2, 4.5 and 6.9 wt% were subjected to surface mechanical attrition treatment (SMAT) to investigate the effect of stacking fault energy (SFE) on the microstructural feature of gradient structure (GS) layers produced by SMAT and back stress hardening during Bauschinger unloading reloading tests. In the GS layer, the alloys with different SFE exhibit various grain morphologies, grain size distributions and densities and distributions of geometrically necessary dislocations (GNDs). Because of these differences in the microstructural features of the GS layers, the alloys show different variations associated with SMAT during the Bauschinger unloading-reloading tests, i.e. the increment of true stress decreases sharply with a decrease of SFE at small strains, while it slightly decreases at large strains. It is found that SFE can significantly affect grain boundary strengthening and back stress hardening to synthetically improve the tensile strength of GS Cu-Al alloys to different levels.