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Abstract
Accumulative roll bonding (ARB) is a severe plastic deformation process for sheet metals. The process can produce ultra fine-grained structures by repeatedly joining and rolling of similar and dissimilar metal sheets through many cycles. In the current investigations, commercial purity aluminium alloy (AA1050) consisting of 32 layers was produced using up to 5 ARB cycles. The aim of the current study is to understand the microstructural and textural evolution during deformation (ARB) and the recrystallization behaviour upon subsequent annealing of this alloy. The majority of the analysis was carried out based on the data generated by electron backscatter diffraction (EBSD) analysis. It has been shown that the deformation in ARB is largely influenced by the amount of redundant shear strain generated in each cycle. Therefore, a tailored experiment was designed specifically to measure the amount of the redundant shear strain in each cycle.
In studying the deformation of ARB, EBSD analysis was carried on both the central and sub-surface regions. In general, three stages of the microstructural development process were identified, which will eventually lead to the formation of ultra fine-grained structure. The current material also showed a certain level of dynamic recovery after the first few ARB cycles via the reduction in the fraction of low angle grain boundaries (LAGB). Due to the influence of the redundant shear strain, inhomogeneous microstructure was identified at a low number of ARB cycles. However, the homogenous microstructure found at higher number of ARB cycles is due to the effect of both localized strain hardening and the natural processing cycle in ARB.
Upon annealing, the sample that was processed with 5 ARB cycles recrystallized discontinuously. Microstructural heterogeneity and the pre-existent cube texture was deemed to be the reason for such behaviour. In two separate annealing done for different durations, the overall grain size remained similar and no significant microstructural change was detected. It is possible that fine oxide particles or alloy precipitates could have caused Zener pinning and prevented the grain growth. The recrystallized texture showed an increase in cube orientation, while the rest of the typical rolling textures, which existed before annealing were destroyed.