Solute diffusion in Al-rich binary alloys was studied by means of atomistic simulations. The activation energy for the diffusion of Mg in the bulk was evaluated, in the dilute-solution limit, for nearest-neighbor and ring mechanisms. It was concluded that bulk diffusion at low and moderate temperatures had to be assisted by vacancies. The diffusion of Mg along the cores of edge, 60° and screw dislocations was studied. The activation energy for vacancy formation in the core, and for vacancy-assisted Mg migration, was evaluated for a large number of diffusion paths in the core region. It was observed that, as in the bulk, Mg diffusion in the absence of vacancies was energetically disfavored. The paths of minimum activation energy were identified, for vacancy-assisted diffusion, for all 3 types of dislocation. The lowest-energy path was found in the core of the 60° dislocation. Its activation energy was equal to 60% of that for the bulk. Most of the diffusion paths had activation energies that were greater than 75% of the equivalent bulk value. These data showed that pipe diffusion, which was considered to be the main mechanism of dynamic strain aging, was too slow in the absence of excess vacancies.

Atomistic Study of Pipe Diffusion in Al–Mg Alloys. R.C.Picu, D.Zhang: Acta Materialia, 2004, 52[1], 161-71