Regulating strength and ductility of gradient-structured Cu–Al–Zn via SMAT and annealing

For most metallic materials, the surface mechanical attrition treatment (SMAT) resulted in a substantial increase in the yield strength, but accompanied by a certain decrease in the ductility. However, the regulating of the yield strength and ductility in the gradient-structured Cu–Al–Zn alloys by the SMAT and annealing was less studied systematically. In this study, the microstructural evolution and mechanical properties of gradient-structured Cu–Al–Zn alloys with different stacking fault energy (SFE) after annealing were systematically investigated. The tensile properties show that the SMAT Cu–Al–Zn alloys with low SFE after annealing at 320 °C for 20 min exhibits a superior combination of strength and ductility. The microstructure characterizes reveal that the density of dislocations is decreased in the SMAT Cu–Al–Zn alloys with low SFE after annealing, meanwhile the degree of accumulated dislocations on the deformed twins is also weakened and maintains deformation twins feature, which thus achieve a superior balance of yield strength and ductility. Further analysis demonstrates that the annealed SMAT Cu–Al–Zn alloy with low SFE still maintains an obvious HDI strengthening. Furthermore, the digital image correlation (DIC) results indicate that during tensile deformation, gradient-structured Cu–Al–Zn alloys with low SFE can form dispersed strain bands, which contributes to improved ductility. This study provides a feasible strategy for regulating the strength and ductility of gradient-structured copper alloys.