Kinetic Monte Carlo simulation of clustering in an Al-Zn-Mg-Cu alloy (7050)

A kinetic Monte Carlo technique using a simple vacancy jump for atomic diffusion has been employed for the first time to simulate early-stage precipitation in an Al-Zn-Mg-Cu (7050) alloy. Using interaction parameters deduced from the matrix compositions in over-aged samples measured using 3-dimensional atom probe, the simulation has successfully reproduced early-stage metastable GPI zone precipitation behaviour including evolution of the cluster chemistry, the cluster number density and cluster size. The simulation has revealed the effect of strong Mg-vacancy interaction on the composition of small clusters and has indicated that there is Zn enrichment of some clusters, which further explains previous experimental observation of smaller GPI zones transforming to η' precipitates