Diffusion of ⁶⁵Zn in dilute AlCu, AlCuZn, AlSi, and AlSiZn alloys

Abstract

The diffusion coefficients of ⁶⁵Zn have been measured in dilute AlCu, AlCuZn, AlSi and AlSiZn alloys as a function of the concentration and temperature in the range of solid solutions. The ⁶⁵Zn diffusion coefficients depend linearly on the Cu and Si concentration and the enhancement effects of the different solutes investigated are additive.

The experimental values–together with previous results for ⁶⁵Zn diffusion in dilute AlZn, AlMg and AlZnMg alloys (Beke et al. 1977)–are interpreted on the generalization of the model given by Le Claire (1978) and it is found that the tracer jump frequencies in the vicinity of the solutes change only by a factor less than 2. Furthermore, supposing that the jump frequencies are unaltered and the solute-solute binding are also negligible, an approximate expression can be obtained for the enhancement factor which contains only the solute-vacancy binding energy B _t,v. From this relation the following approximative values were obtained B _zn,v = 0.03 ± 0.01 eV, B _Mg.v = 0.02 ± 0.02 eV, B _Cu,v = 0.03 ± 0.02 eV and B _Sl.v = 0.04 ± 0.02 eV.

From macroscopic models based on the generalization of the law of corresponding states for diffusion in binary alloys (Beke et al. 1979) it is found that the calculated enhancement factors are in good agreement with the experimental values. Furthermore, the conclusions drawn from this model confirm the results of microscopic models: the solutes investigated cause only small perturbations for aluminium and only weakly affect the jump frequencies of the zinc tracer.