Diffusion of Solutes in Aluminum and Dilute Aluminum Alloys

Diffusion of impurities in single crystals of aluminum and dilute aluminum alloys has been studied by tracer-sectioning techniques. In pure aluminum, the activation energies for Au, Ag, Cd, and Fe are (in kcal/mole) 27.0±0.11, 28.0±0.014, 29.7±0.26, and 46.0±1.4. The pre-exponential factors are (in ${\mathrm{cm}}^2$/sec) 0.077, 0.13, 1.04, and 135. The values for Ag and Au agree with other available data, while those for Cd and Fe disagree with previously reported anomalous results, which apparently were perturbed by surface oxide. When 1% of various solutes are added to aluminum, sizable enhancements are observed in the diffusion coefficients of Cu and Ag. This is understood in terms of increased jump rates caused by the Friedel oscillations in the screening potential about impurities.