Atomic-scale pathway of early-stage precipitation in Al–Mg–Si alloys

Strengthening in age-hardenable alloys is mainly achieved through nano-scale precipitates whose formation paths from the atomic-scale, solute-enriched entities are rarely analyzed and understood in a directly verifiable way. Here, we discover a pathway for the earliest-stage precipitation in Al–Mg–Si alloys: solute clustering leading to three successive variants of face-centered cubic (fcc) clusters, followed by the formation of non-fcc GP-zones  . The clusters, which originally assume a spherical morphology (C1C1), evolve into elongated clusters and orient themselves on {111}Al{111}Al (C2C2) and subsequently on {100}Al{100}Al planes and 〈100〉Al〈100〉Al directions (C3C3). We also analyze the association of quenched-in dislocations with clustering phenomena. The results of this work can open a new frontier in advancing alloy-process-property design for commercially important age-hardenable Al alloys.