Abstract
In this work, the mechanical behaviour and microstructure changes of AA-7075 alloy subjected to a repetitive-bending-under-tension (R-BUT) process were studied. In the R-BUT process, a metallic strip undergoes repeated localised bending and unbending. Load-displacement curves derived from R-BUT tested samples displayed a drastic increase in elongation to failure as compared to samples subjected to standard tensile tests. Additionally, the results confirmed that the force required to deform the R-BUT samples is much reduced as compared to the load required during simple tension. Finite element analysis confirmed that the sample subjected to the R-BUT process underwent intense shear deformation. Transmission-electron-microscopy (TEM) and electron-backscattered-diffraction (EBSD) analysis of the deformed matrix from the ND-RD plane (through-thickness) exhibited evidence for the formation of fine grains. TEM analysis confirmed that the fine grains formed were in the size range of 200–400 nm. Intense shear deformation experienced by the matrix led to shearing followed by spheroidization of precipitate particles. The influence of precipitate particles on the grain refinement process through Particle Stimulated Nucleation of fine grains in the matrix is also presented. EBSD analysis suggested that a Continuous Dynamic Recrystallisation process is the key mechanism behind the grain refinement in the sample during R-BUT processing.
Highlights
Thriving human populations, globalisation and global warming have made both the manufacturing sector and consumers focus on technologies to produce products which can be recyclable, reduce carbon emission, be cost-effective and flexible to accommodate future demands
There are a range of processes that are classified as inducing severe plastic deformation, these include equal channel angular pressing (ECAP) [2,3], incremental equal channel angular pressing (I-ECAP) [4,5], high pressure torsion (HPT) [6,7], accumulative roll bonding (ARB) [8,9]
It should be noted that the loading condition, as well as the microstructure state, can control the appearance of Portevin-Le Chatelier (PLC) effect in these materials i.e. the appearance of the PLC effect in these materials is influenced by presence of precipitates and test temperature, as well as strain rate
Summary
Globalisation and global warming have made both the manufacturing sector and consumers focus on technologies to produce products which can be recyclable, reduce carbon emission, be cost-effective and flexible to accommodate future demands. Multi axial forging (MAF) [10,11], repetitive corrugation and straightening (RCS) [12,13], twist extrusion (TE) [14,15] and constrained groove pressing (CGP) [16,17] Some of these are used primarily for research, others to produce low volume components. Lee et al calculated the shear straining introduced by different passes of ARB and correlated this to the grain size distribution through the Al sheet thickness [18]. It has been shown how shear straining distributed through the sheet thickness in the different cycles of RCS changes the microstructure of aluminium sheet [19]. In the following CGP cycle this shear straining increases and impacts on the microstructure of the aluminium sheets [16]
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