Diffusion in ultrafine-grained Al-Mg alloys

Grain sizes of less than 1 μm were produced in Al-0.2%Sc (or 0.2%Zr) and Al-3%Mg-0.2%Sc (or 0.2%Zr) alloys using the technique of equal-channel angular pressing (ECAP). These alloys were coupled and they were subjected to diffusion annealing at a temperature in the range of 523 to 773 K. Interdiffusion coefficients were determined from the concentration gradients measured across the interface and a comparison was made with those of coarse-grained diffusion couples. Interdiffusion coefficients of the fine-grained couples are significantly higher than those of the coarse-grained couples at lower annealing temperatures. Grain boundary diffusion coefficients of Mg in Al were deduced from the measurements.