Effect of stacking fault energy on deformation mechanisms in Cu and Cu-30% Zn alloy with gradient structure obtained by SMAT

•After SMAT, the grains on the surface were found to be refined, which were responsible for the increase of yield strength.•In addition, deformation twins formed in the hetero-interface layer of Cu-30%Zn samples due to low SFE during SMAT.•The high density of GNDs in Cu-30%Zn indicates twins can hinder the movement of dislocations and store more dislocations.•Combining high strength and good ductility is due to the HDI strengthening and HDI hardening caused by GNDs. The deformation mechanism and mechanical properties of pure copper and copper-zinc alloys with low stacking fault energy (SFE) were investigated primarily. In this paper, pure Cu and Cu-30%Zn samples were processed by surface mechanical attrition treatment (SMAT) at cryogenic temperature. The results show that Cu-30%Zn samples exhibit higher yield strength and better ductility by tensile tests at room temperature. With the same processing time of SMAT, the SMAT-ed Cu-30%Zn samples exhibit an optimized combination of strength and ductility compared with that of the SMAT-ed Cu samples. The in-situ electron backscatter diffraction (EBSD) tests show that there is a high density of geometrically necessary dislocations (GNDs) in SMAT-ed Cu-30%Zn samples with low SFE, thereby forming a strong hetero-deformation induced (HDI) stress strengthening and HDI hardening. Also, the twins promote the accumulation of geometrically necessary dislocations to enhance strength while maintaining good ductility in the Cu − 30%Zn samples.