Strength and ductility synergy in a ‘sandwich structure’ Cu–Al alloy with multi-gradient structure

The strength-ductility 'trade-off' has become a long-term dilemma of metal structural materials. Gradient structure is a unique hierarchical system that can reduce stress concentration effectively and achieve a synergistic improvement of strength and ductility. In this work, a multi-gradient structure (including gradient stacking fault energy, gradient grain size and gradient interface) was established in Cu–Al alloys via powder metallurgy technique. The tensile testing results show that the 'sandwich structure' Cu–Al alloy with multi-gradient structure possesses excellent mechanical properties (yield strength of ∼180.6 MPa, engineering ultimate tensile strength of ∼344.2 MPa and engineering strain of ∼57.9%), higher than the values predicted by the rule of mixture (ROM). The gradient stacking fault energy leads to the formation of gradient microstructure during deformation, and contributes to the combination of high strength and good ductility. The gradient interfaces can reduce effectively the stress concentration and thus provide the ability of continuous work-hardening. The gradient grain size also provides extra work hardening ability. All the three gradient structures collectively contribute to the high strength and large ductility.