Tensile deformation of mechanically milled Al-1.1Mg-1.2mol%Cu was carried out at 523 to 823K using a true strain-rate of 1/s. The largest uniform elongation before local necking occurred at 748K. This temperature dependence of the uniform elongation was analyzed from a strain hardening viewpoint, in which a balance of stored dislocations and their thermal recovery was responsible for maintaining a high mobile dislocation density that was sufficiently temperature-dependent to permit a high uniform elongation. It was found that the thermal activation process of liberating unlocked immobile dislocations from solute atmospheres was responsible for the temperature dependence of the thermal recovery of stored dislocations. The same process applied to deformation parameters such as the re-mobilization probability of immobile dislocations and the mobile dislocation density. These were previously obtained from analyses of the stress-strain behavior on the basis of dislocation dynamics. The activation energy of about 32kJ/mol was equivalent to the vacancy migration energy in Al, minus the binding energy between a vacancy and a Mg or Cu solute atom.

Thermal Recovery of Dislocations and Nature of Uniform Elongation during High Temperature Deformation of a Mechanically Milled Al-1.1mol%Mg-1.2mol%Cu Alloy. T.Hasegawa, W.Uchino, K.Okazaki: Materials Transactions, 2003, 44[7], 1370-5