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Analysis of strain rate sensitivity of ultrafine-grained AA1050 by stress relaxation test

Mohebbi, M. S ; Sharif University of Technology

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  1. Type of Document: Article
  2. DOI: 10.1007/s11661-014-2534-4
  3. Abstract:
  4. Commercially pure aluminum sheets, AA 1050, are processed by accumulative roll bonding (ARB) up to eight cycles to achieve ultrafine-grained (UFG) aluminum as primary material for mechanical testing. Optical microscopy and electron backscattering diffraction analysis are used for microstructural analysis of the processed sheets. Strain rate sensitivity (m-value) of the specimens is measured over a wide range of strain rates by stress relaxation test under plane strain compression. It is shown that the flow stress activation volume is reduced by decrease of the grain size. This reduction which follows a linear relation for UFG specimens, is thought to enhance the required effective (or thermal) component of flow stress. This results in increase of the m-value with the number of ARB cycles. Strain rate sensitivity is also obtained as a monotonic function of strain rate. The results show that this parameter increases monotonically by decrease of the strain rate, in particular for specimens processed by more ARB cycles. This increase is mainly linked to enhanced grain boundary sliding as a competing mechanism of deformation acting besides the common dislocation glide at low strain rate deformation of UFGed aluminum. Recovery of the internal (athermal) component of flow stress during the relaxation of these specimens seems also to cause further increase of the m-value by decrease of the strain rate
  5. Keywords:
  6. Aluminum ; Backscattering ; Deformation ; Grain boundary sliding ; Mechanical testing ; Plastic flow ; Roll bonding ; Stress relaxation ; Accumulative roll bonding ; Commercially pure aluminum ; Competing mechanism ; Electron backscattering diffraction ; Microstructural analysis ; Plane strain compression ; Strain rate sensitivity ; Stress relaxation test ; Strain rate
  7. Source: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 45, Issue 12 , November 2014 , Pages 5442-5450
  8. URL: http://link.springer.com/article/10.1007%2Fs11661-014-2534-4