Dislocation facilitated surface precipitation in an Al-Cu-Mg thin foil

The preferential surface precipitation of 'tooth-like' Cu-rich nanoprecipitates in an Al-Cu-Mg thin foil after long time natural ageing was revealed by high resolution transmission electron microscopy and electron tomography. These surface nanoprecipitates show an average cross-sectional diameter of similar to 6 nm, and some of them have core-shell structures. The dislocation facilitated solute diffusion, including dislocation assisted pipe diffusion and dislocation movement accelerated solute diffusion, was considered to be the dominant manner for solute diffusion from bulk interior to sample surface during natural ageing. The enrichment of Cu rather than Mg in surface nanoprecipitates was attributed to the superior Cu-vacancy binding energy, which can well facilitate Cu diffusion to dislocations. This result highlights the surface effect on element redistribution in nanoscale metallic alloys during long term performance, and provides a guidance for the development of metallic nanodevices.