The diffusion of Cu into the relatively pure Al cladding on commercial Al-Cu-Mg alloys (AA2014, AA2024), at temperatures of 400 to 500C, was characterized by making measurements of etch marker movement and concentration profiles. The latter method furnished lattice interdiffusion coefficients that agreed well with published data. The former method provided information on grain boundary diffusion. The activation energy for this was between 77.5 and 90kJ/mol, and the diffusion coefficients were between 105 and 3 x 105 times greater than those for lattice diffusion. For grain sizes of 25 to 50μ, boundary diffusion was of primary importance at long diffusion times; with the bulk diffusion being amenable to analysis by means of the Hart equation.

Lattice and Grain-Boundary Diffusion of Copper into Cladding on Alclad Al-Cu-Mg Alloy Sheet R.C.Dorward: Materials Science and Technology, 1998, 14[3], 187-92