Atomistic simulations of early stage clusters in AlMg alloys

The Cluster Expansion formalism based on Density Functional Theory (DFT) simulation data has been applied for AlMg alloys with high accuracy ($\sim 1$ meV/atom). The atomistic simulations are used to model the AlMg 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 γ-phase are in accordance with the experimental phase diagram. The calculations demonstrate the formation of Guinier-Preston (GP) zones of ${\text{Al}}_3\text{Mg}$ (L$1_2$ phase) within the Al matrix under varying conditions. The computed transition temperatures where the ordered structures dissolve are approximately $50\text{K}$ 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.