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An Investigation into Creep Behavior and Cavitation in a 7000-Series Aluminum Alloy

Safarloo, Sama | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53574 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Serajzadeh, Siamak
  7. Abstract:
  8. In this study, creep behavior and cavitation as well as high temperature deformation of Al-Zn-Mg aluminum alloy were investigated by means of uni-axial creep and tensile tests. The as-received material i.e. AA7075 plate, was first stabilized utilizing over-aging heat treatment and then stress-controlled creep tests were performed in the temperatures ranging between 120℃ to 210℃ under the applied stresses varying 130MPa to 250MPa. Accordingly, the stress exponent and creep activation energy were determined as 5.7 and 149kJ/mol.K to 189kJ/mol.K, respectively. Considering these parameters, it was found that the governing creep mechanism, in the mentioned temperature range, would be dislocation climb. Also, a model based on two-dimensional cellular automata was developed for prediction of cavitation during creep deformation. To do so, the results of optical metallography and scanning electron microscopy were employed to define the material parameters used in the simulation. In the other part of this research, deformation behavior of the alloy was studied at elevated temperatures. In the first place, the alloy was subjected to solid solution heat treatment at 475℃ for 2 hr. and then the tensile tests were conducted in the temperatures varying between 100℃ to 350℃ under different strain rates. In the next step, the occurrence of dynamic precipitation and softening processes during hot deformation were determined. The achieved results illustrated that dynamic precipitation could occur in temperatures less than 125℃ under low strain rates i.e. of order of 10-3 or less, leading to negative strain rate sensitivity. In addition, dynamic recovery and dynamic recrystallization were detected to be operative at temperatures higher than 200℃ and 350℃, respectively. Hot deformation activation energy was also calculated as 274.2 kJ/mol as well as the processing maps were defined using the dynamics material modeling together with the experimental data and a neural network model
  9. Keywords:
  10. Hot Deformation ; Creep Behavior ; Cavitation ; Aluminum Alloy Series 7xxx ; Cellular Automata ; Aluminum Alloy 7075

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