Atomistic simulations of early stage clusters in Al-Mg alloys

The Cluster Expansion formalism based on Density Functional Theory (DFT) simulation data has been applied for Al-Mg alloys with high accuracy (similar to 1 meV/atom). The atomistic simulations are used to model the Al-Mg phase diagram, phase boundaries and the initial solute clustering at different compositions and temperatures. The obtained free energies of formation for the FCC, HCP and gamma-phase are in accordance with the experimental phase diagram. The calculations demonstrate the formation of Guinier-Preston (GP) zones of Al3Mg (L1(2) phase) within the Al matrix under varying conditions. The computed transition temperatures where the ordered structures dissolve are approximately 50 K higher than experimental data. The free energy barriers associated with the formation of GP-zones increase as the solute (Mg) concentrations are reduced and the temperature is increased. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.