The effect of zinc and silicon on the rate of diffusion of aluminium

Abstract

The rate of climb of prismatic dislocation loops in thin foils of quenched aluminium-zinc and aluminium-silicon alloys was measured by quantitative transmission electron microscopy and compared with similar measurements made on pure aluminium. The addition of 0.35% silicon or 1.5% zinc to aluminium approximately doubled the climb rate; the significance of these differences was established by statistical analysis. It is concluded that the faster climb rates are caused by solute-enhanced diffusion. This conclusion is consistent with previous diffusion measurements in aluminium-zinc alloys. Combination of the results with N.M.R. data shows that the diffusion enhancement factor decreases as the temperature increases as expected from theoretical considerations. The activation energy for climb appears to be slightly lower in the alloys than in the pure solvent but these differences are only marginal and it is shown that this is consistent with theory. The observations are interpreted in terms of available theories of diffusion in dilute solid solutions. The results indicate that the solute-vacancy interaction energy for zinc is small (<0.1 ev); that for silicon is larger, a tentative estimate being ∽ 0.12 ev.