Unlocking ultrahigh strength in dilute Al alloys: The synergy of stable grain boundary networks and solute clusters

The strength of Al alloys can be significantly enhanced through grain refinement and aging hardening. However, improving strength through aging hardening in nanograins is challenging due to the poor structural stability, which leads to grain growth and precipitation coarsening. Herein, a nanostructured AA6061 alloy with grain size of 26 nm and a high proportion of relaxed grain boundaries (GB) was fabricated using cryogenic high-pressure torsion (HPT). During aging treatment, Mg-Si-Cu co-segregated at GBs and high density of Mg-Si solute clusters (approximately 5.6 × 1023 m-3) rather than intermetallic precipitates formed within the nanograins, resulting in a record strength as high as 805 MPa.