Cooperative effect of strength and ductility processed by thermomechanical treatment for Cu-Al-Ni alloy

Cu-Al-Ni alloys are one class of typical precipitation strengthening alloy, its mechanical properties are highly sensitive to temperature and strain. In this work, the strength-ductility cooperative effect is investigated through a thermomechanical treatment, i.e., unidirectional cold rolling, Split-Hopkinson-Pressure-Bar deformation, and aging treatment. The results show that a large number of dislocations and twin structures are introduced during Split-Hopkinson-Pressure-Bar deformation motivated by the high strain rate (2.5 x 103 s-1). When the treat-ment temperature is slightly lower than the elongation peak (-28.66%, which almost surpasses all existing Cu-Al-Ni alloys) aging temperature, a high strength (-797.06 MPa) is also achieved. The strength-ductility optimization process mainly includes two mechanisms, twining/grain boundaries optimization, and second-phases optimization, which are closely related to dislocations movement and can contribute together without conflict. In addition, a phase-field-crystal method is used to dynamically display the interaction between twins and dislocations. Finally, the typical characteristics of this kind of high strength-ductility copper alloys are proposed, namely, small grain size, high twin density, and stable grain boundary, providing more space for the cooperative improvement of strength and ductility in Cu alloys.

Automated summary

This work investigates the strength-ductility cooperative effect of Cu-Al-Ni alloys through thermomechanical treatment. The results show that high strain rate induces the introduction of dislocations and twin structures, and high strength can be achieved at a slightly lower temperature than the elongation peak. The optimization of strength-ductility mainly involves twining/grain boundaries optimization and second-phases optimization, which contribute together without conflict. The interaction between twins and dislocations is dynamically displayed using a phase-field-crystal method. The typical characteristics of high strength-ductility copper alloys include small grain size, high twin density, and stable grain boundary.