Achieving maximum strength-ductility combination in fine-grained Cu-Zn alloy via detwinning and twinning deformation mechanisms

Abstract

• The FG Cu-30%Zn was prepared by ECAP and subsequent annealing. • The optimal strength and ductility combination was achieved. • Microstructural evolutions during tensile deformation were revealed by EBSD. • Deformation-induced detwinning of pre-existing ultrafine twin lamellae occurred. • Grain orientation with< 111 > // TD facilitates deformation twinning. Although deformation twinning has been demonstrated to improve the strain hardening and ductility of metals and alloys with low stacking fault energies (SFEs), the optimum grain size for maximum strength-ductility combination still needs to explore. In this work, we selected Cu- 30 wt% Zn alloy with extremely low SFE (7 mJm -2 ) acting as a model material. Specifically, Cu- 30 wt% Zn samples with different grain sizes ranging from 628 nm to 30.6 µm were prepared by equal-channel-angular pressing (ECAP) and subsequent annealing. Tensile test revealed that the maximum strength-ductility combination (ultimate tensile strength of 565 MPa and ductility of 20%) corresponds to a mean grain size of 3.8 µm. Electron backscatter diffraction (EBSD) indicated that pre-existing annealing twins in fine-grained Cu- 30 wt% Zn alloy annihilated at the initial deformation stage (<10% tensile strain) via detwinning of thin twin lamellae (<1 µm) and conversion of twin boundaries of thick twin lamellae (>1 µm) into conventional high-angle grain boundaries. In the later stage of deformation (>10% strain), deformation twinning occurred in grains with<111>orientation parallel to tensile direction, suggesting the combination of both detwinning and twinning deformations caused the maximum strength and ductility synergy. Our findings provide insights into optimization of strength and ductility of metals with low SFEs and detwinning-twinning deformation mechanisms.