Loading...

Simulation of Retrogression Process Effect on Mechanical Properties and Formability of Precipitation-Hardenable Aluminum Alloys

Ebrahimi, Hossein | 2023

85 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 56393 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Karimi Taheri, Ali
  7. Abstract:
  8. A common heat treatment used for hardenable aluminum alloys is the retrogression process. In this process, by dissolving a specific precipitate in the alloys (η'), the strength of the alloys is reduced and their formability is enhanced. However, by applying the retrogression process and deforming the alloy, followed by an aging cycle, the strength returns to its original state. In this project the microstructural evolution during the retrogression process in 7075-aluminum alloy has been primarily studied experimentally with the help of a transmission electron microscope and the effect of retrogression time on the microstructural evolution has been assessed. In addition, since the simulation of microstructural changes helps to predict the behavior of the material, a phase-field model framework is developed to simulate the retrogression process in the alloy. The model predicts the dissolution kinetics of the η' phase during the retrogression process. The input parameters of the model are achieved from the experimental tests, calphad-based thermodynamic simulations, and molecular dynamics studies. To validate the model, the average radius and size distribution of η' precipitates obtained from the phase-field model were compared with the results obtained from the transmission electron microscope. Both experimental and simulation results indicated that after retrogression for 100 seconds, at 200°C, only a small percentage of precipitates are completely dissolved and the hardness of the alloy can be recovered by a secondary aging process. By increasing the retrogression time to 500 seconds, most of the precipitates are completely dissolved, and as a result, the hardness of the material cannot be recovered by a secondary aging process. As the retrogression process influences the mechanical properties and formability of the alloy through removing the η' precipitates and reducing the amount of the matrix-precipitate interface in the microstructure, in this project in order to investigate this effect, the uniaxial tensile tests at different retrogression times were performed on the alloy. Then, using the Abaqus software and with the help of the ductile fracture model, these tests were simulated and the amount of the optimum initial void volume, corresponding with the experimental results, was predicted. After that, by applying this optimum initial void volume, the forming limit diagrams of the alloy, at different retrogression times, were predicted. The results of simulations exhibited that the retrogression process significantly reduces the volume of voids in the alloy, and as a result, it enhances the formability of the alloy
  9. Keywords:
  10. Aluminum Alloy 7075 ; Transmission Electron Microscope ; Phase Field Model ; Mechanical Properties ; Formability ; Retrogression Process ; High Strength Alloy ; Precipitation Hardenable Aluminum Alloy

 Digital Object List

 Bookmark

No TOC