Dislocation engineering via Al3(Sc,Zr)-mediated coarse low-angle grain boundaries for breakthrough strength-ductility balance in Al-Zn-Mg alloys

• Heterogeneous microstructure with 80.5% LAGBs via Sc/Zr-mediated thermomechanical processing. • Synergistic strengthening from η′ precipitates and LAGBs enabled 554 MPa strength with 17.2 % elongation. • Molecular dynamics validated LAGB-dislocation interactions as critical for strain delocalization. • Design framework for overcoming strength-ductility trade-offs in high-stacking-fault-energy alloys. The strength-ductility trade-off in Al-Zn-Mg alloys remains a critical challenge for advanced structural applications. In this work, we present a novel microstructural design strategy integrating Sc/Zr microalloying with thermomechanical processing to engineer a heterogeneous structure dominated by coarse low-angle grain boundaries. Through multi-pass hot rolling and tailored aging, an Al-6.7Zn-2.3 Mg-0.2Sc-0.1Zr alloy achieved an exceptional tensile strength of 554 ± 6 MPa and uniform elongation of 17.2 ± 0.8 %, surpassing conventional counterparts. Advanced characterization techniques, including electron backscatter diffraction and transmission electron microscopy, are employed to reveal that the coherent Al 3 (Sc,Zr) precipitates exhibit superior thermal stability and effectively restrict dislocation motion. Molecular dynamics simulations have shown that the coarsening of low-angle grain boundaries is primarily due to the dislocation storage effect. Appropriate aging treatments result in uniformly dispersed η′ phases, which enhance the alloy’s strength through the synergistic effects of dislocation cutting mechanisms and coherency. This study establishes a paradigm for achieving a balance between strength and ductility in aluminum alloys via grain boundary engineering at LAGBs, offering valuable insights for the design of heterostructured materials aimed at high-performance applications.