Enhancing strength-ductility synergy of Cu alloys with heterogeneous microstructure via rotary swaging and annealing

The trade-off of strength and ductility in the Cu alloys seriously restricts its wide application. In this study, the paradox of strength and ductility of the Cu alloy is ameliorated by rotary swaging (RS) and subsequent annealing, and reveals its microstructural evolution. It was found that the grain size was obviously refined after the RS, resulting in yield strength as high as 719 MPa but with a ductility of only 2.4 %. After annealing, the RS-350-20 sample (RS sample annealed at 350 °C for 20 min) exhibited partial recrystallization at the edge and middle positions, while full recrystallization occurred at the center position, which formed a gradient grain size distribution. Tensile results showed that RS-350-20 sample exhibited an excellent combination of the yield strength of 495 MPa and ductility of 27 %. High strength stemmed from residual deformation grains, recrystallized ultrafine/fine grains and heterogeneous deformation-induced (HDI) strengthening. The good ductility originated from recrystallized coarse grain, pronounced HDI hardening and activated deformation twins. In addition, microstructural characterization further revealed that dislocations were accumulated near the recrystallized grains to maintain strain continuity at the interface of deformed grains and recrystallized grains during tensile strain. With increasing strain, deformation twins were activated near the recrystallized grains, which facilitates high strain hardening capability meanwhile maintaining high strength. These findings provide insight for optimizing the strength and ductility of Cu alloys by a feasible processing.