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The Effect of Cu Powder during Friction Stir Welding of Severely Deformed Al on the Microstructure and Mechanical Properties

Kiani Renani, Behzad | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53478 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kokabi, Amir Hossein; Kazeminezhad, Mohsen
  7. Abstract:
  8. In order to increase the strength of metals such as aluminum, severe plastic deformation processes can be used. Due to the fact that the dimensions of their products are usually small due to limitations, the connection of severely deformed sheets can be considered. Friction stir welding seems to be suitable for this purpose as a solid state process, but due to the significant amount of strain energy stored in this type of sheet, after recrystallization in the stir zone and the surrounding areas often experience severe grain growth. In this research, the 1050 aluminum sheets are severely deformed by constrained groove pressing (CGP) process were subjected to friction stir welding. Microstructure investigations showed that in the stir zone, welded specimens without copper powder formed equiaxed grains that were much larger than the grain size of the base metal, indicating the occurrence of grain growth after dynamic recrystallization it is in the mentioned area. The use of copper powder during friction stir welding leads to the formation of intermetallic compounds in the stir zone, which increases the hardness of the stir zone. In addition, with increasing the number of passes and the rotational speed of welding, the type and amount of intermetallic compounds formed also increased. Also, at high rotational speeds of welding, the presence of copper powder acts as a source of heat absorption and prevented severe grain growth and hardness drop in the stir zone. Microstructure investigations showed that the presence of copper powder also controls the intensity of grain growth in the thermo mechanically affected zone and heat affected zone. In addition investigation the fracture surface of welded specimens with and without copper powder showed that at high rotational speeds the place of fracture has changed from the thermomechanical zone to the heat affected zone. It is worth noting that at low rotational speeds the presence of copper powder had little effect on ultimate tensile strength. However, at high rotational speeds, the presence of copper powder has a significant effect on increasing strength. This also showed that the presence of copper powder from a critical point onwards can control grain growth and before that it has little effect on controlling grain growth
  9. Keywords:
  10. Friction Stir Welding ; Severe Plastic Deformation ; Copper Powder ; Aluminum Alloy 1050 ; Microstructural Refining

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