Evolution of nanoscale precipitates in Al microalloyed with Sc and Er

The coarsening kinetics of nanoscale, coherent Al3(Sc1-xErx) precipitates in α-Al during aging of a supersaturated Al–0.06 Sc–0.02 Er (at.%) alloy at 300 °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 °C, the α-Al/Al3(Sc1-xErx)α-Al/Al3(Sc1-xErx) interfacial free energy due to Sc is about twice as large as for α-Al/Al3Scα-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.