Diffusion of gold and copper in aluminum

Abstract

The diffusivities of gold and copper in pure aluminum were determined by residual-activity method with radioactive tracers (Au198and Cu64) in the range of temperature between 290∼650°C and 375∼ 619°C, respectively. Almost all the penetration curves of both gold and copper in aluminum were found to consist of three regions, which represented near-surface effect, volume diffusion, and short-circuit diffusion, respectively. All the three regions were distinctly observed at low temperatures, but the near-surface effect disappeared at high temperatures. The dependence of diffusion coefficients of gold and copper on temperature were given by the following equations: [formula omitted] and [formula omitted] The pre-exponential factor and activation energy for diffusion of gold in aluminum were very similar to those for diffusion of aluminum, copper, silver, and zinc in aluminum, and it was suggested that the volume diffusion of gold in aluminum occurred by single vacancy mechanism. The diffusivities of gold in aluminum were found rather greater than those of aluminum and copper in aluminum. Such a difference of diffusivities between the both would be due to the variation in activation entropy. Although gold has extremely low solid solubility in aluminum, the characteristics of the diffusion of gold in aluminum was substantially different from those of other elements in particular, transition elements which are slightly soluble in aluminum where the short-circuit diffusion takes precedence of the volume diffusion. The present result provided one of the best examples that the behavior of impuritydiffusion was not thoroughly ex-Plained only by low solubility The diffusivities of copper in aluminum derived from the results of the present work were in good agreement with the results in the past. Therefore, the procedures of the present work in experiments and analyses were proved to be satisfactory. © 1970, The Japan Institute of Light Metals. All rights reserved.