An internal friction peak vs temperature has been observed around 260°C (| = 1 Hz) in cold-twisted and partially annealed AlMg solid solutions. Internal friction peak vs strain amplitude appears around the temperature region of this peak. Systematic studies have been made on the effect of deformation, annealing, bias-stress, Mg content and ageing treatments. The activation energy associated with this peak was found to be close to that of the bulk diffusion of Mg atoms in aluminium. A dislocation-kink Cottrell atmosphere model is suggested according to which this new peak (P3 peak) is attributed to the stress-enhanced long-ranged diffusion of the Mg solute atoms constituting the Cottrell atmosphere around the dislocation kink chain introduced in the specimen by twisting deformation.