Dual effect of Cu on the Al3Sc nanoprecipitate coarsening

It is generally considered that the Al3Sc nanoprecipitates are highly thermal stable, mainly due to quite slow Sc diffusion in the ci-Al matrix. In this paper, we demonstrate in an Al-Cu-Sc alloy that the Cu atoms have dual effect on the coarsening of Al3Sc nanoprecipitates. On the one hand, the Cu atoms with high diffusivity tend to accelerate the Al3Sc coarsening, which results from the Cu-promoted Sc diffusion. On the other hand, some Cu atoms will segregate at the Al3Sc/matrix interface, which further stabilizes the Al3Sc nanoprecipitates by reducing the interfacial energy. Competition between these two effects is tailored by temperature, which rationalizes the experimental findings that the coarsening kinetics of Al3Sc nanoprecipitate is greatly boosted at 300 degrees C-overaging while significantly suppressed at 400 degrees C-overaging. (C) 2019 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.