Loading...

Modeling the Microstructure Evolution and Mechanical Properties of Al-Mg-Si alloys During Thermomechanical Treatment

Anjabin, Nozar | 2013

765 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 45151 (07)
  4. University: Sharif University
  5. Department: Materials Science and Engineering
  6. Advisor(s): Karimi Taheri, Ali
  7. Abstract:
  8. The Al-Mg-Si alloys are an important group of industrial materials used extensively in the automotive and aerospace industry, due to their high strength to weight ratio, good corrosion resistance and the recycle ability. In order to achieve a combination of optimized microstructure and properties during the production processes, the study of deformation behavior and heat treatment of these alloys is necessary. Therefore, the prediction of microstructural evolution and mechanical properties as a function of alloy chemical composition and thermomechanical treatment is important for these alloys, from both the scientific and industrial aspects. In the present research, the flow behavior of this group of aluminium alloys was studied both experimentally and theoretically at different deformation and heat treatment conditions. To do so, in the first step, the precipitation kinetics and important features of precipitates were predicted as a function of chemical composition, aging temperature and time. Then, the mechanical properties of the alloy were assessed as a function of deformation conditions and previous heat treatment using the dislocation density based and crystal plasticity constitutive modeling. Finally, the modeling results were compared with the appropriate experimental data. According to the achieved results, the work hardening behavior of the alloy is completely different for different aging conditions. The overaged sample has the highest initial work hardening rate, due to the presence of geometrically necessary dislocations. In this condition, due to the relaxation processes, flow stress reaches a steady state value after small strains, while under aged samples continue to work hardening to higher strains. Considering the flow behavior of single crystals containing precipitates, using the crystal plasticity modeling approach, exhibited difference between flow stresses of different crystal orientations, is lower for the overaged samples compared to the quenched samples. This difference is partly related to the precipitate induced anisotropy and partly to the saturation of flow stress due to relaxation processes. Also, the rotation of precipitates at high strain, depending on the orientation of the precipitates relative to the loading direction, can increase or decrease the crystallography anisotropy. Considering the dynamic strain aging of quenched alloy, it was found that depending on the deformation temperature and strain rate, two mechanisms including dynamic precipitation and solute pinning, can be responsible for dynamic strain aging. The proposed model could predict the serrated flow and nucleation and propagation pattern of the localized deformation bands, observed experimentally
  9. Keywords:
  10. Ageing Kinetics ; Aluminum-Magnesium-Silicon Alloy ; Flow Behavior ; Crystal Plasticity ; Finite Element Method ; Microstructure Evolution

 Digital Object List

 Bookmark

No TOC