مشخصات پژوهش

Stress-relieved Al-Mn-Si specimens were constrained groove pressed (CGPed) and in the following, coldrolled under different strains of 0.47, 0.8 and 1.27. Dual strained sheets were isothermally heat treated at 150, 250, and 350 C. Microstructure survey revealed that generated shear-bands by CGP acted as talent sites for further strain-induced grain boundary migration (SIGBM) during annealing. SEM micrographs pointed out that coarse particles (1 mm <) had not preferential positions within the aluminum matrix and often comminuted into fine dispersoids (0.5 mm >) under heavy strains. Assessment of the softening fraction (Rrec) depicted that greater accumulated strains along with higher post-annealing temperatures accelerated the thermal recovery and hence, reduced the Rrec. Tensile testing was performed repeatedly while fluctuation range for obtained stress-strain curves for each specimen as a criterion of structural uniformity was considered. It was found that post-deformation treatment of severely deformed sheets at 250 C supplied maximum structural uniformity due to perfect restoration and evolution of inhomogeneity agents such as shear-bands, and precipitates within the matrix. In this regard, processing route contained cold-rolling by 0.8 strain of two-pass CGPed specimen and subsequent annealing at 350 C ascertained to be an adequate combination of deformation and heat treatment with respect to achievement of the maximum uniform elongation (UE) of 22.96% and contribution of uniform deformation energy (UD) in total mechanically absorbed energy equal to 84.18% that provided the optimal formability for the applied alloy. Fracture analysis was performed by fracture angle measurement and SEM fractography. Thermal annealing of CGPed sheet at 150 and 250 C declined its fracture angle from 55 to 50 and 46.5, respectively. However, annealing at 350 C changed the dominant fracture mode from shear to necking by incidence of fibrous morphology and enhanced the angle