Oxidation-vacancy production in aluminium alloys

Abstract

Abstract The climb of prismatic dislocation loops in dilute aluminium alloys has been investigated as a function of alloying addition by isothermal annealing of thin foils. It was observed that the loops annealed out by shrinking in all the alloys investigated except for aluminium-magnesium where loop growth occurred. It is proposed that the vacancy supersaturation necessary for the observed growth is due to the production of vacancies in the surface regions of the foil as magnesium atoms become absorbed by a growing surface oxide film. This model has been critically examined by investigating the rate of growth as a function of annealing time, annealing temperature and the oxygen pressure of the annealing environment. The results confirm this model of vacancy production and show that in the alloys containing 0·65% magnesium, diffusion of magnesium to the surface regions is the rate-controlling process whereas in the more concentrated alloys (3·3% and 6·6% Mg) surface oxidation is rate controlling.