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Mechanical Properties and Microstructure of Severely Deformed Thin Copper Sheet as the Middle Layer in Constrained Groove Pressing Process

Panjipour, Amir Hossein | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58132 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kazeminejad, Mohsen
  7. Abstract:
  8. The deformation of thin sheets in grooved dies is accompanied by certain limitations, primarily due to the fine serrations of the die. These serrations create stress concentration, inducing shear deformation in the thin sheet. In this study, to apply severe plastic deformation to a 1-mm-thick copper sheet, two additional 1-mm-thick sheets were used as outer layers on either side of the copper sheet. The copper sheet served as the middle layer, while the outer layers consisted of aluminum sheets in one series of experiments and low carbon steel sheets in another. This approach enabled the investigation of the influence of the outer layer hardness on the mechanical properties and microstructure of the copper sheet during severe deformation. Additionally, to enhance the mechanical properties of the thin copper sheets, the samples were annealed under two conditions: once in the as-deformed state in the grooved die, and again after three passes at three different temperatures 200°C, 300°C, and 400°C. This allowed for a simultaneous evaluation of the effects of annealing temperature and number of passes on the mechanical behavior and microstructure of copper. The results indicated that, in general, using outer layers with lower hardness than the middle copper layer such as aluminum reduced the feasibility of deformation in the grooved die due to premature failure of the outer sheets. Conversely, the use of harder steel sheets improved the ability to induce severe deformation in the thin copper sheets. Ultimately, the yield strength, ultimate tensile strength, and hardness of the samples were measured. The highest values of hardness and strength were observed in the samples annealed at 300°C. Specifically, the maximum yield strength (260 MPa) and ultimate tensile strength (285 MPa) were recorded in samples subjected to one-pass deformation and annealed at 300°C. Moreover, by controlling the annealing time and applying the optimal temperature of 300°C, the smallest microstructure with an average grain size of 8 microns was achieved after two passes in the copper samples between steel sheets. Overall, the results demonstrate that using harder outer layers around the thin middle layer, combined with proper annealing and optimized pass numbers, leads to improved mechanical strength compared to single-layer samples. This enhancement is attributed to reduced stress concentration during deformation
  9. Keywords:
  10. Severe Plastic Deformation ; Copper ; Microstructure ; Mechanical Properties ; Thin Plates ; Constrained Groove Pressing (CGP)

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