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The Relationship between Microstructure and Mechanical Properties of AA1050/MMO Nanocomposite Fabricated by Friction Stir Processing

Alishavandi, Mahdi | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50214 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kokabi, Amir Hossein
  7. Abstract:
  8. Ultra-fine and fine-grained aluminum matrix nano-composites were fabricated by friction stir processing (FSP) of 1050 Al alloy sheets containing 6 vol% volume fractions of pre-inserted MMO nanoparticles. Annealed sheets were processed at different rotational (w=800-2000 rpm) and traverse speeds (v-50-200 mm/min). A special design tool (concave shoulder and cylindrical pin with regular threads) without changing the rotation and traveling directions was utilized. It is shown that the best and highest desired mechanical properties of the base metal is attained at w=1600 rpm and v =100 mm/min through one single pass. The structure of grains are changed due to the applied severe plastic deformation, which ultimately affect the mechanical properties of the processed sheets. While the microstructure of the annealed aluminum alloy consists of a coarse grain structure, FSP results in a deformed grain structure containing cuboidal and spherical MMO particles. A discontinuous dynamic recrystallization process is involved for the annealed sheets after FSP. Examinations of the mechanical properties of the Al sheets indicate significant improvement in Vickers hardness and tensile strength with utilizing 8 vol% volume of the MMO concentrations. Although higher hardness values are attained at higher MMO, concentrations, the tensile strength is remarkably reduced. Fractographic studies determine a change in the fracture mode from completely ductile rupture for the Al alloy before and after FSP to a ductile-brittle fracture for the nano-composites. Evaluation of wear characteristics by a pin on disk setup displays an enhanced wear resistance and friction coefficient by incorporating of the nanoparticles in the metal matrix. The role of grain strengthening of the examined materials boundaries and dislocations found to be more effective on the strengthening that Orowan looping
  9. Keywords:
  10. Aluminum Alloy ; Mechanical Properties ; Microstructure ; Nanocomposite ; Mischmetal ; Friction Stir Welding ; Aluminum Alloy 1050 ; Strengthening (Metal)

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