Achieving superior strength-ductility trade-off in heterostructured Al-Zn-Mg-Cu-Zr alloys via the mediation of trace TiB2 nucleants

Designing heterogeneous structure (HS) is becoming an emerging strategy to enhance the strength and ductility synergy of metallic materials. For 7xxx series aluminum alloys, however, it usually relies on complex thermomechanical treatments, which is highly challenging. In this study, by precisely controlling the TiB2 particle contents in Al-Zn-Mg-Cu-Zr alloys and combining conventional deformation and heat treatment, the residual large-sized Al2CuMg phases after homogenization are utilized to synergize with TiB2 particles to promote dynamic recrystallization (DRX) nucleation during deformation. Meanwhile, the combined pinning effect of Al3Zr dispersed phases and TiB2 on dislocations and sub-grain boundaries is employed to suppress recrystallization grain growth. Through the coordinated control of nucleation and growth processes, three types of heterogeneous lamellar structures with precisely controllable recrystallization volume fractions (11.2-45.2 vol.%) are successfully constructed. When the TiB2 content is up to 0.5 wt.%, 7055-TB5 formed a heterogeneous lamellar structure with a recrystallization volume fraction of 23.3 vol.%, demonstrating an excellent strength-ductility combination (tensile strength of 779 MPa and elongation of 13%). This study has opened up a novel path to break the strength-ductility inversion dilemma of Al-Zn-Mg-Cu-Zr alloys and broadened the application prospects of HS materials.