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A Study on the Effect of Initial Microstructures on Deformation Behavior of an Aluminum-Copper Alloy at Elevated Temperatures

Molaei, Soheil | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55430 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Serajzadeh, Siamak
  7. Abstract:
  8. In this research, hot deformation and creep behavior of aluminum alloy i.e.AA2017 were taken into account while the impact of the initial microstructure of the examined alloy was also studied. In order to investigate the behavior of the alloy, tensile tests were conducted at temperatures ranging from 120°C to 400°C under the nominal strain rates of 0.0005 s-1, 0.005 s-1, 0.05 s-1. In these experiments, two different initial microstructures were employed including solution treated samples as well as artificially aged specimens. The results show that in the temperature range of 180°C to 250°C, the strain rate sensitivity parameter is negative in the solution treated samples which indicates the occurrence of dynamic precipitations during deformation. In the other hand, dynamic recrystallization at low strain rates was operative temperature higher than 350°C. Using hyperbolic sine equation, the stress power was computed as 9.1 and the apparent activation energy for hot deformation 444 in the temperature range of 300°C to 400°C. Also, by examining the results of the creep tests in the temperature range of 120°C to 250°C and the applied stress of 150 MPa to 270 MPa, the stress power greater than 5.5 and the activation energy of 169 kJ/mol were achieved. These demonstrate that the governing mechanism of creep could be the climb of dislocations. By examining the optical, XRD and scanning electron microscopic images, it was observed that during creep deformation, the suitable places for cavity formation were the triple points, around the second phase particles as well as grain boundaries. In the next step, with the help of the obtained results and physical models, the mechanisms of deformation and softening in the temperature range of 120°C to 250°C for aging samples and two temperatures of 150°C and 180°C were studied. the stress power greater than 5.5 and the activation energy of 169 kJ/mol. Employing the dynamic material modeling together with the neural network, the processing maps were constructed at temperatures above 250°C and the hot workability for examined sample was also studied and accordingly, the proper hot deformation conditions were assessed
  9. Keywords:
  10. Creep ; Hot Deformation ; Aluminum Alloy 2017 ; Hot Tension ; Creep Behavior ; Aluminum-Copper Alloy

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