Isochronal annealing of as received aluminium wires of commercial purity is carried out from room temperature up to 600 "C. The results show the existence of two annealing stages, one from room temperature up to 300 "C and the other from 300 "C upwards. The first annealing stage with an activation energy of 0.2 eV is interpreted by vacancy-silicon binding energy and clustering of Si atoms on grain boundaries. The second annealing stage is proved to be a multi-energy stage with an activation energy ranging between 0.36 and 0.80 eV, this is in agreement with that for the Si diffusion in the aluminium matrix during the recrystallization process. The wires are then subjected to combined tensile-torsion deformation. The results show (i) negative tensile strain ( -A L / L ) i.e. contraction for samples annealed over the temperature range of the first annealing stage. This behaviour is inferred to hardening due to internal stresses formed on clustering of Si atoms a t grain boundaries, as well as the formation of Luders bands at the grain boundaries during twisting, (ii) normal positive tensile strain (+ AL/L) for samples annealed over the temperature range of the second annealing stage. This behaviour is attributed to the decrease in the internal stresses; because annealing a t these relatively high temperatures (above 300 "C) leads to the diffusion of Si atoms collected a t grain boundariesa t the first annealing stagein the matrix.Un recuit isochronal a Btk effect& pour l'aluminium de la temperature ambiante jusqu' L 600 "C.Les rbsultats obtenus montrent que le recuit s'effectue en deux &tapes; la premiere de la tempbrature ambiante L 300 "C, et la deuzikme au delh de 300 "C. Pendant la premiere &ape 1'6nergie d'activation est Bgale L 0,2 eV interpretbe comme &ant 1'6nergie de liaison de silicium-lacune et de rassemblement d'atomes de Si les sur joints de grains. Tandis que pour la deuzikme Btape 1'6nergie d'activation n'est pas constante; elle est de 0,36 L 0,SOeV en accord avec celle de diffusion de Si dans la matrice d'aluminium pendant le processus de recristallisation. Des Bchantillons prealablement recuit sont soumis a la deformation en torsion-traction. Les rBsultats obtenus montrent: (i) une deformation detraction negative ( -A L / L ) dans le domaine de la premiere Btape. Ce comportement est attribuB au durcissement dB aux contraintes internes produites par le rassemblement des atomes de Si sur les joints de grains aussi que par la formation des bandes de Liider pendant torsion; (ii) une deformation de traction normale (+AL/L) pour les Bchantillon prerecuits pour la deuzieme Btape. Ce comportement est attribue L la diminution des contraintes internes; le recuit A ces temperatures provoquera la diffusion des atomes de Si rassembles sur les joints de grains (pendant la premikre &ape de recuit) dans la matrice.
Pure tensile and combined torsion–tension deformation experiments are made using Al–0.72% Si samples of different grain diameters. Plastic instability behaviour is observed in the case of combined torsion–tension deformation. The onset and disappearance of this instability is found to depend on some parameters, as mode of deformation, applied axial tensile stress, working temperature, sample grain diameter, and quenched‐in vacancies.
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