  The grain boundary (GB) microchemistry and precipitation behaviour in
high-strength Al-Zn-Mg-Cu alloys has an important influence on their mechanical
and electrochemical properties. Simulation of the GB segregation,
precipitation, and solute distribution in these alloys requires an accurate
description of the thermodynamics and kinetics of this multi-component system.
CALPHAD databases have been successfully developed for equilibrium
thermodynamic calculations in complex multi-component systems, and in recent
years have been combined with diffusion simulations. In this work, we have
directly incorporated a CALPHAD database into a phase-field framework, to
simulate, with high fidelity, the complex kinetics of the non-equilibrium GB
microstructures that develop in these important commercial alloys during heat
treatment. In particular, the influence of GB solute segregation, GB diffusion,
precipitate number density, and far-field matrix composition, on the growth of
a population of GB precipitates, was systematically investigated in a model
Al-Zn-Mg-Cu alloy of near AA7050 composition. The simulation results were
compared with scanning transmission electron microscopy and atom probe
tomography characterisation of alloys of the similar composition, with good
agreement.
