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.