Tensile strain and resistance variation caused by torsional deformation in dilute Al-Mg alloys

Pure tensile and combined torsion-tension deformation has been investigated for three Al-Mg alloys: (Al+0.50wt%Mg), (Al+0.85wt%Mg) and (Al+1.60wt%Mg). Plastic instability behavior 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 applied axial tensile stress, working temperature and sample grain diameters. The influence of plastic deformation on the electrical resistivity for such materials has been investigated at room temperature. Both torsion-tension deformation and electrical resistivity were found to decrease on plastic straining for samples as received, and pre-annealed from 373 till 573 K, and then it increased for samples pre-annealed at 673 K and 773 K. The results show negative tensile strain (ΔL/L0) for samples annealed in the temperature range of the first annealing stage which is inferred to hardening due to internal stresses formed on clustering of Mg atoms at grain boundaries as well as the formation of Luders bands at the grain boundaries during twisting. The positive result observed for samples pre-annealed at higher temperature is attributed to dispersion of Mg precipitates inside the grains during the recrystallization process.