ON THE ROLE OF Mg ATOMS ON THE RECOVERY OF COLD-WORKED Al-5.5 AT, % Mg

Abstract

Internal friction and thermo-mechanical analysis pointed towards the existence of four annealing stages in the recovery of cold-worked Al-5.5 as % Mg alloy in the temperature range from 25 to 300°C. The first annealing stage, activated by an energy of 0.63 eV, was attributed to the annealing of vacancy-Mg couples formed during cold-working . By increasing the annealing temperature these vacancy-Mg couples started to form complex aggregates that led to the appearance of an absorption band in the annealing spectrum. The mechanisms responsible for these two recovery stages were enhanced by pre-annealing. Recrystallization started at temperatures about 110°C showing itself as another annealing band activated by an energy of 1.42 eV. Mg solute atoms acting as impurity-pinning points, retarded the dislocation mobility and correspondingly the recrystallization process. The binding energy between the Mg-solute atoms and dislocations was found to be 0.22 eV. The annealing stage appearing at higher temperature was charaterized by a large activation energy (1.62 eV) and was attributed to the tendency of Mg atoms to form clusters in the Al-matrix.