Anomalous SAXS and APT investigation of core–shell precipitation in Al–Mg–Sc–Zr alloys

Abstract

Understanding the compositional evolution of core–shell ${\mathrm{L1}}_2$ ${\mathrm{Al}}_3$(Sc,Zr) precipitates in aluminium alloys is critical for tailoring their mechanical performance. In this study, we combine atom probe tomography (APT) and anomalous small-angle X-ray scattering (ASAXS) to characterise, for the first time, the in situ chemical evolution of these precipitates during a two-step ageing treatment. APT confirms the sequential formation of a Sc-rich core followed by a Zr-enriched shell, while ASAXS, conducted near the Zr K-edge, enables time-resolved tracking of Zr incorporation during precipitation. Two alloys with and without Mg were compared to investigate the effects of Mg on the precipitation kinetics, morphology of precipitates and strengthening behaviour.