Evolution of nanoscale precipitates in Al microalloyed with Sc and Er

The coarsening kinetics of nanoscale, coherent Al-3(Sc1-xErx) precipitates in alpha-Al during aging of a supersaturated Al-0.06 Sc-0.02 Er (at.%) alloy at 300 degrees C are studied using transmission electron microscopy and local-electrode atom-probe tomography. Erbium and Sc segregate at the precipitate core and shell, respectively. The matrix supersaturations of Er and Sc, as well as the mean precipitate radius and number density evolve in approximate agreement with coarsening models, allowing the determination of the matrix/precipitate interfacial free energy and solute diffusivities. At 300 degrees C, the alpha-Al/Al-3 (Sc1-xErx) interfacial free energy due to Sc is about twice as large as for alpha-Al/Al3Sc. The diffusivity of Er in the ternary alloy is about three orders of magnitude smaller than that of Er in binary Al-0.045 at.% Er and about two orders of magnitude smaller than the diffusivity of Sc in binary Al-Sc. The measured Sc diffusivity is consistent with the literature values. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.