Thermal Recovery of Dislocations and Nature of Uniform Elongation during High Temperature Deformation of a Mechanically Milled Al-1.1 mol%Mg-1.2 mol%Cu Alloy

Abstract

Tensile deformation was carried out for a mechanically milled Al–1.1 mol%Mg–1.2 mol%Cu alloy at temperatures of 523–823 K and a true strain rate of 1×10⁰ s⁻¹. The largest uniform elongation prior to local necking occurred at an intermediate temperature (748 K). This temperature dependence of the uniform elongation was analyzed from a strain hardening viewpoint in which the balance of the stored dislocations and the thermal recovery of them is responsible for maintaining a high mobile dislocation density that is exclusively temperature-dependent to sustain a large uniform elongation. It was found that thermal activation process of liberating unlocked immobile dislocations from solute atmosphere is responsible for the temperature dependence of thermal recovery of stored dislocations. The same process applies for the deformation parameters such as the re-mobilization probability of immobile dislocations and the mobile dislocation density that were previously obtained from the analysis of stress-strain behavior on a basis of dislocation dynamics. An activation energy of approximately 32 kJ/mol is equivalent to the vacancy migration energy in aluminum minus the binding energy between a vacancy and a solute atom of magnesium or copper.