Solution potential measurements were used to determine Cu concentrations at the surface of Alclad 2014 sheet, after heat treatment at temperatures ranging from 400 to 500C. It was found that the interdiffusion coefficients which were calculated from the concentration versus time dependence were 5 to 10 times greater than those for lattice diffusion. The apparent activation energy (85kJ/mol) was also appreciably lower than that (125kJ/mol) for lattice diffusion. The discrepancy was attributed to grain boundary effects, and calculated effective diffusion coefficients agreed closely with experimental data.

R.C.Dorward: Journal of the Electrochemical Society, 1997, 144[3], L33-6