Diffusion of 65Zn in dilute AlZn, AlMg, AlZnMg and AlZnFe alloys

Abstract

The diffusion coefficients of 65Zn have been measured in dilute AlZn, AlMg, AlZnMg and AlZnFe alloys in the function of concentration and temperature in the ranges 0,…, 4 at.%Zn, 0,…, 6.6 at.%Mg, 0,…, 0.1 at.%Fe and 360, …,660°C, respectively. The results in pure aluminium are in agreement with earlier data in the literature. The 65Zn diffusion coefficient depends linearly on the zinc concentration in AlZn alloys and the enhancement factors b 21 Zn increase with decreasing temperature. In the investigated AlMg alloys the zinc diffusion is enhanced about half as much by magnesium as by zinc and the enhancement factors show a similar temperature dependence as in the case of the AlZn alloys. The enhancement effects of the zinc and magnesium solute in AlZnMg are additive in the investigated solid solution range. The experimental values are interpreted on the basis of the model given by Miller [5] and corrected by Warburton [4], and it was obtained that h Zn = (0.049 ± 0.006) eV and h Mg = (0.028 ± 0.009) eV m the alloys AlZn and AlMg. respectively, where h Zn and h Mg are the binding energies of a zinc atom and a magnesium atom to the zinc-vacancy pair. The results for AlZn alloys could be interpreted on the basis of Stark's calculations [6] too, but here the values of the enhancement factors could only be estimated, since the binding energy between two zinc atoms is unknown. The diffusion coefficients of 65Zn in AlZnFe alloys are practically independent of the iron concentration. In all investigated alloys the diffusion coefficients measured satisfy well the Arrhenius equation.