Interface-engineered Al-Zn-Mg-Cu alloys with Sc/Zr-assisted high-ratio TiB₂ refinement for enhanced mechanical performance

In-situ synthesized TiB₂ particles serve as effective heterogeneous nucleation sites for refining grain size of aluminum (Al) alloys. However, excessive TiB₂ content induces self-agglomeration, thereby diminishing the grain refinement efficacy on the Al matrix. Here, we demonstrate that trace additions of Sc/Zr could effectively refine TiB₂ particles, mitigating agglomeration at elevated TiB₂ concentrations. The refinement of TiB₂ particles subsequently enhances their grain refinement efficacy on the Al matrix. As a result, Sc/Zr microalloying improves ultimate tensile strength of as-cast TiB₂/Al-Zn-Mg-Cu alloys by 51 % and elongation by 91 %. Detailed electron microscopy analysis reveals that Sc/Zr microalloying forms nanoscale L1₂-structured Al₃(Sc,Zr) precipitates with ultra-low lattice misfit to α-Al, enabling coherent α-Al/Al₃(Sc,Zr)/TiB₂ multi-interfaces for efficient heterogeneous nucleation and grain refinement. The Al₃(Sc,Zr) can simultaneously pin grain boundaries and suppress recrystallization. The synergetic effects of Sc/Zr and TiB₂ on the microstructure and mechanical properties of the Al-Zn-Mg-Cu alloys were systematically discussed.