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Constrained groove pressing, cold-rolling, and post-deformation isothermal annealing: Consequences of their synergy on material behavior

Pouraliakbar, H ; Sharif University of Technology | 2018

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  1. Type of Document: Article
  2. DOI: 10.1016/j.matchemphys.2017.12.010
  3. Publisher: Elsevier Ltd , 2018
  4. Abstract:
  5. Stress-relieved Al-Mn-Si specimens were constrained groove pressed (CGPed) and in the following, cold-rolled 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 μm <) had not preferential positions within the aluminum matrix and often comminuted into fine dispersoids (0.5 μm >) 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 to 61°. Likewise, it was revealed that in spite of fracture angle increment by rolling reduction, post-rolling prevented the necking fracture in CGPed sheet treated at 350 °C and this might be shifted to higher temperatures. © 2017 Elsevier B.V
  6. Keywords:
  7. Annealing ; Fracture analysis ; Mechanical properties ; Microstructure ; Severe plastic deformation (SPD) ; Aluminum compounds ; Aluminum sheet ; Cold rolling ; Fracture mechanics ; Grain boundaries ; Isothermal annealing ; Isotherms ; Manganese ; Manganese compounds ; Metal cladding ; Precipitates ; Rolling ; Shear bands ; Silicon compounds ; Stress-strain curves ; Tensile testing ; Thermal oil recovery ; Constrained groove pressing ; Post-annealing temperature ; Severe plastic deformations ; Strain induced grain boundary migration ; Structural uniformity ; Uniform deformation ; Uniform elongation ; Fracture
  8. Source: Materials Chemistry and Physics ; Volume 206 , 2018 , Pages 85-93 ; 02540584 (ISSN)
  9. URL: https://www.sciencedirect.com/science/article/abs/pii/S0254058417309586