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Additive Manufacturing of Aluminum Matrix Composite by Friction Stir Method

Nasrollahi, Amir Hossein | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57011 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Movahedi, Mojtaba
  7. Abstract:
  8. Considering the unique characteristics of aluminum alloys in the 5XXX series, such as high strength-to-weight ratio and corrosion resistance, as well as the absence of precipitation hardening, composite fabrication using these alloys has garnered attention. Consequently, friction stir additive manufacturing (FSAM), a novel solid-state layering technique, has been proposed for manufacturing components from these alloys, avoiding the drawbacks associated with traditional melt-based additive manufacture methods. The objective of this research is to produce a five-layer 20mm composite wall in the aluminum 5754 substrate using iron powder via FSAM to achieve desirable mechanical properties. To address existing challenges, with the optimal distribution of reinforcement particles and the resulting property dependency being the most critical, the influence of tool rotational speed (700 to 1500 rpm) and interlayer passes (1 to 5 passes) was investigated. Microstructural analysis of the friction-stir-processed region, including grain size and particle distribution, was performed using optical and electron microscopy. Additionally, electron backscatter diffraction was employed to examine fracture surfaces. Mechanical properties of the composite were evaluated through tensile tests and microhardness measurements. The results indicate that increasing the number of passes from one to five leads to a better and more symmetrical distribution of reinforcing powder in the processed region, significantly reducing agglomeration of particles. Improved powder distribution contributes to finer grain sizing in the processed region. This phenomenon generally holds true for an increase in rotational speed from 700 to 1500 rpm, for the specific case of a 3-passes specimens, increasing the rotation speed from 700 to 1100 rpm is accompanied by a significant rise in agglomeration and input heat due to grain coarsening. Consequently, for the 3-passes specimens, an optimal behavior is observed at 700rpm compared to 1100rpm. Single-pass processing not only fails to enhance properties but also leads to a degradation of properties compared to the base metal. However, an increase in the number of passes results in improved tensile strength relative to the base metal. The highest tensile strength and elongation for the composite resulting from 5-passes and a rotational speed of 1500 rpm are recorded as 276 MPa and 24%, respectively. These values represent a 47% increase in tensile strength and a 68% increase in elongation compared to the base metal. The fracture surfaces of the tensile specimens exhibit ductile failure modes, confirming the effectiveness of the friction stir additive manufacturing (FSAM) process in achieving desirable mechanical properties. Furthermore, with increased uniformity in the microstructure and reduced agglomeration of particles at higher rotational speeds and a greater number of passes, finer dimples are formed, resulting in a more ductile behavior. Additionally, intermetallic compounds such as Al3Fe and Al5Fe2, formed through reactions between iron powders and the aluminum substrate, have been identified. The microhardness graphs exhibit reduced oscillation and enhanced symmetry with an increasing number of passes. Furthermore, hardness values are consistently observed across most points within the friction stir zone
  9. Keywords:
  10. In-Situ Composite ; Intermetallic Compounds ; Microstructure ; Mechanical Properties ; Additive Manufacturing ; Friction Stir Welding ; Aluminum-Ferrite Composite

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