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A Study on Hot Deformation and Kinetics of Softening in an Aluminum Alloy (AA5052)

Navid Moghadam, Nasim | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53501 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Serajzadeh, Siamak
  7. Abstract:
  8. In this work, the deformation behavior of an Aluminium-Magnesium alloy i.e. AA5052, in different temperature ranges was studied experimentally and theoretically. For this purpose, uniaxial tensile tests were carried out in the temperature range of 25°C to 450°C and under strain rates of 0.001 "s-1" to 0.05 "s-1" . Also, the occurrence of dynamic strain aging and dynamic softening mechanisms of the alloy were taken into account. It was observed that the dynamic strain aging occurred in the temperature range of 25°C to 125°C while the corresponding activation energy was defined as 46.2 kJ/mol which is close to migration of Mg atoms in aluminum. At hot deformation region, different softening mechanisms including dynamic recovery and dynamic recrystallization were also detected. It was found that the dynamic recrystallization would be operative at temperatures higher than 400°C and also, the apparent activation energy for hot deformation was computed as 192.06 kJ/mol using hyperbolic-sine constitutive equation. Moreover, an artificial neural networks was trained in order to predict the stress behavior of the alloy under various strain raters and temperatures. In the next stage, by using results of the ANN modeling, corresponding processing maps were developed and the workability of the material was investigated. In the other part of this work, a two-dimensional simulation was conducted employing the Cellular Automata coupled with the ANN modeling. Accordingly, the occurrence of dynamic recrystallization during hot deformation and resulting microstructural changes were predicted. Moreover, the activation energy of grain nucleation and grain growth were determined as 175 kJ/mol and 210 kJ/mol, respectively. It should be noted that optical microscopy, scanning electron microscopy, and Vickers hardness tests were also used for microstructural studies, determination of material constants, and validation of the simulation results. Comparison between the predicted and real microstructures demonstrated a reasonable agreement indicating that validity of the employed model and solution algorithm. Finally, by using the finite element method and Abaqus software, the isothermal open-die forging process was simulated and coupled with the developed microstructural mode
  9. Keywords:
  10. Cellular Automata ; Aluminum Alloy 5052 ; Microstructure Simulation ; Dynamic Recrystallization ; Softening Kinetics ; High Temperature Deformation ; Aluminum-Magnesium Alloy

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