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Modification of Surface Nanostructure and Mechanical Properties by Friction Stir Processing in Al 5083 with Al2O3 and Cu Particles

Khaksari, Mehdi | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41367 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kokabi, Amir Hossein; Akbarzadeh Changiz, Abbas
  7. Abstract:
  8. Al 5083 is a non-heat treatable alloy that widely used in the aerospace and automotive industry due to its low density and high strength. However, poor wearing behavior and low elastic modulus restrict its engineering applications. Metal matrix composites (MMCs) have advantages of high strength and modulus by reinforcement of second phase. Also, MMCs have excellent dimensional stability, damping capacity and wear, creep and fatigue resistances as compared with the corresponding monolithic alloys. Vast loss in ductility and toughness occurs by non- deformable ceramic reinforcements. For the surface engineering purposes, ceramic particles are added in the surface layers of components, whereas the bulk maintains the primary composition and structure with higher ductility. Fatigue and corrosion resistances, strength and formability are increased by structure modifications through Friction Stir Processing (FSP). FSP is also used to fabricate the MMCs and superplastic materials. FSP is a solid state process which decreases the harmful reaction between the metal matrix and reinforcing agent and causes microstructure refinement. In this work, fabrication of MMCs with FSP is achieved by two methods First, direct adding of reinforcing particle and second, in situ formation of reinforcement during FSP. It is observed that sound surface composite can be produced with tool rotation rates of 800-1400 rpm, tool travel speed of 30-90 mm/min and tool tilt of 3o. Increasing the rotational speed at constant traverse speed leads to increase of the heat input and also provides higher shear force that helps to decrease Al2O3 particle size and to disperse them in a wider region. Increasing FSP passes leads to separation of particles from each other and decrease of the average grain and particle size. After four FSP passes, the hardness of Al 5083/ Al2O3 nano-composite was increased up to 50% and the UTS was increased from 281 to 358 MPa. At next stage, Al 5083/ Al2CuMg composite was produced with nano-scale Cu powder by four FSP passes. The pin on disc wear test shows that weight loss is decreased in surface composite layer, as compared to the initial alloy. It is shown that reinforcement prevents matrix plastic deformation and changes the wear mechanism from adhesive to abrasive-adhesive
  9. Keywords:
  10. Aluminum ; Wear Resistance ; Friction Stir Welding ; Copper Nanoparticles ; Aluminum Alloy 5083 ; Aluminum Oxide Nanoparticle

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