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 (Cl), evolve into elongated clusters and orient themselves on {111}(Al), (C2) and subsequently on {100}(Al) planes and < 100 >(Al) directions (C3). 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. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.