Experimental and DFT characterization of η′ nano-phase and its interfaces in Al-Zn-Mg-Cu alloys

The structures and energetics of eta' nano-phase and its interfaces in a peak-aged Al-Zn-Mg-Cu alloy were thoroughly investigated, using the combination of aberration corrected HAADF-STEM imaging and first-principles calculations. The most feasible atomic structure of eta', along with the solute substitution in eta', were calculated and compared with the atom resolution Z-contrast images. The interface phase diagram of eta'/Al was constructed as a function of the excess chemical potential of Zn, to determine the equilibrium interface structures. Solute segregation to these interfaces was further calculated, and the results were adopted to interpret the experimental Z-contrast images. Finally, all the bulk and interface results were integrated to predict the solute partition in the matrix and further its potential impacts on interface properties, and based on which, a new strategy was proposed for future optimal design of Al-Zn-Mg-Cu alloys. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.