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Microstructure and Mechanical Properties of Hybrid Aluminum Matrix Composite Reinforced by Graphite Particles and Zirconium Oxide Nanoparticles Fabricated by Friction Stir Processing

Keshavarz, Hossein | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54644 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kokabi, Amir Hossein
  7. Abstract:
  8. In this research, aluminum matrix composites (AMCs) reinforced by different contents of zirconium dioxide nanoparticles, graphite microparticles, and a mixture of both with various hybrid ratios, into a cold-rolled Aluminum1050 as base metal, fabricated by 4-passes friction stir processing. Observations show that the processing of composites reinforced by Gr particles is significantly hard due to the low friction coefficient of graphite resulting in the decline in the maximum temperature during the process and the type of base metal. The mixtures of graphite and zirconia resulted in more homogenous dispersion of particles in the matrix due to deterring a drastic drop in friction coefficient and in the tendency of the nanoparticles agglomeration than mono-composites. Also, increasing the temperature and severe plastic deformation during FSP accelerates dynamic recovery (DRV) and dynamic recrystallization (DRX), which brings up fine and equiaxed grains in the stir zone. X-ray diffraction (XRD) analysis demonstrated the formation of Al3Zr intermetallic compounds during Al/ZrO2 nanocomposite fabrication due to in-situ reactions. Tensile tests and microhardness measurements showed that the ultimate tensile stress, yield stress, and microhardness of composites gradually improved by increasing the weight percent of the secondary phases. Hence, the ultimate tensile strength of the Al-9 wt.% ZrO2, Al-2 wt.% Gr, and Al-3 wt.% (Gr + ZrO2) with a hybrid ratio of (Gr/ZrO2 =2) have increased 41.49%, 52.28, and 32.1% compared to the base metal, respectively. On the other hand, the elongation, especially in graphite-reinforced composites, decreased after four passes FSP to the extent that the %elongation of Al-2 wt.% Gr composite declined up to 46.47% compared to the base metal
  9. Keywords:
  10. Aluminum Matrix Composite ; Friction Stir Processing ; Lubrication ; Graphite ; Zirconia ; Strengthening (Metal)

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