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Investigation of Mechanical Properties and Microstructure of Al/Fe3O4 Nano Composite Produced by Friction Stir Processing

Eftekhari, Meisam | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48000 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kokabi, Amir Hossein; Movahhedi, Mojtaba
  7. Abstract:
  8. Friction Stir Processing (FSP) was used to fabricate Al1050/Fe3O4 nanocomposite in three different weight percent (2.5%, 4% and 5.3%). The effects of rotational speed (1200-1600 rpm), traverse speed (5-15 cm/min) and the number of FSP passes (1, 2, 3 and 6 passes) on microstructure and mechanical properties were investigated. In order to study microstructure evolution, optical and field emission scanning electron microscopes were used. Micro hardness, longitudinal and transverse tensile and wear test were carried out to investigate mechanical properties of the obtained composites. Results showed that increase of the rotational speed and decrease of the traverse speed in 1 pass processed sample led to increase in the grain size. However in 3 passes processed sample, just enhancement the rotational speed resulted increase of the grain size and traverse speed did not affect the grain size in a regular manner. In other hand, increase of the rotational speed and FSP passes caused uniform distribution of Fe3O4 particles in the matrix. The solid state reactions between the aluminum matrix and reinforcing particles also led to formation of Al-Fe intermetallics. Due to the rotation of the tool, intermetallic layer was broken and distributed in the matrix resulting the formation of in-situ composite from Al matrix and Al-Fe intermetallics. By investigation of the reaction layer and using of other researches, Al3Fe and Al5Fe2 were supposed to be formed. From the viewpoint of the average heat input and achieving maximum strength, the rotational speed of 1400 rpm and the traverse speed of 10 cm/min were chosen as optimum variables. The micro hardness and ultimate tensile strength (UTS) of the composite prepared by the mentioned speeds and after six passes increased about 64% and 27%, respectively. Also it was observed that the UTS of the nanocomposite with 4 wt% (optimum weight percent) increased 62%. Moreover, it was observed that the fracture behavior of all the FSPed specimens with Fe3O4 particles was a mixture of brittle and ductile modes. Investigation of the transverse tensile test results confirmed that the distribution of the Fe3O4 particles had a significant role on the strength of the nanocomposite. Pin on disc wear test results indicated that the nanocomposites had better wear resistance in comparison to as-received Al1050. The nanocomposite produced by six FSP passes showed maximum wear resistance
  9. Keywords:
  10. Wear Test ; Tensile Test ; Nanocomposite ; Friction Stir Welding ; Aluminum Alloy 1050 ; Iron Oxide ; In-Situ Composite

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