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The Effects of Severe Plastic Deformation and Annealing Treatment on Mechanical Properties and Microstructure of AA2024 Alloy Containing Precipitates

Asadi, Saeed | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44902 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kazeminezhad, Mohsen
  7. Abstract:
  8. Improvement of mechanical properties and microstructure of 2024 aluminum alloy by performing a severe plastic deformation method, called multidirectional forging (MDF), and heat treatment was the aim of this research. In this work the effects of heat treatment before and after deformation on mechanical properties and microstructure of the alloy were studied.
    Microstructure evolution during severe plastic deformation was considerably affected by the precipitates and non-shearable particles. On the other hand, the severe plastic deformation had different effects on precipitates in the microstructure and precipitation processing after deformation. Fragmentation, scattering and dissolution of precipitates and acceleration the kinetics of precipitation during ageing after deformation were the examples of these effects. Also, stability of the deformed samples during annealing was heavily influenced by these second phase particles.
    Microstructure was studied by optical, scanning electron microscope (SEM) and X-ray diffraction. The study of X-ray diffraction patterns of samples after 8 passes of MDF by the Williamson-Hall method showed that the cell size for the annealed samples was decreased to 310 nm while this value was 270 nm for the overaged samples. Also, SEM images showed that fragmentation and scattering of precipitates had occurred in widespread. The mechanical properties with shear punch test and hardness test were studied. Applying 2 passes of MDF in super saturated samples resulted in dynamic precipitation and consequently shear strength was increased up to 70%. The results of hardness and shear punch test illustrated that hardness and shear strength of samples were heavily increased by applying MDF. These increasing were 55% for the annealed samples and 40% for the overaged samples after 8 passes. Also, the study of thermal stability showed that the microstructures and mechanical properties were stable up to 300 oC. Finally, the work hardening behavior was studied using a dislocation-based model
  9. Keywords:
  10. Heat Treatment ; Severe Plastic Deformation ; Aluminum Alloy 2024 ; Annealing Heat Treatment

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