Using grain boundary engineering to evaluate the diffusion characteristics in ultrafine-grained Al-Mg and Al-Zn alloys

Samples of dilute Al-Mg and Al-Zn alloys, containing a minor Sc addition, were processed by equal-channel angular pressing (ECAP) to achieve grain refinement and different distributions of the grain boundary misorientations. Diffusion experiments were conducted on fine-grained alloys with either low or high fractions of grain boundaries having high-angle misorientations and on unpressed coarse-grained samples. The diffusion couples were annealed at temperatures from 493 to 848 K and the interdiffusion coefficients were determined from the concentration profiles using the Boltzmann-Matano technique. The results show the interdiffusion coefficients tend to be higher in fine-grained alloys having high fractions of high-angle boundaries than in fine-grained alloys having high fractions of low-angle boundaries. The experimental data are used to estimate values for the grain boundary diffusion coefficients.