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Friction Stir Additive Manufacturing of Al 6061 Aluminum Alloy

Moshtaghi, Amir Keyvan | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58524 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pouranvari, Majid; Kokabi, Amir Hossein
  7. Abstract:
  8. Considering the metallurgical challenges of aluminum alloy AA6061 in fusion-based additive manufacturing methods—such as solidification cracking, methods based on super-plastic deformation, which do not involve fusion and solidification challenges of this alloy, have gained attention for additive manufacturing of AA6061. This method based on super-plastic deformation is the FSAM process. The objective of this study is to investigate the effect of increased thickness resulting from Friction Stir Additive Manufacturing (FSAM) on the mechanical properties of the underlying layers, as well as to examine changes in mechanical properties along the build direction for samples with thicknesses ranging from 6 mm to 15 mm, made of AA6061 alloy. To join the layers, a tool with a rotational speed of 1500 rpm and a traverse speed of 10 cm/min was used. Samples consisting of two to five layers were fabricated. To analyze microstructural variations along the thickness of the five-layer samples, an optical microscope was employed. Additionally, X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FE-SEM) were utilized to examine the morphology of secondary phase particles, crack formations, and fracture surface characteristics along the sample thickness. To evaluate mechanical properties in building direction, tensile testing, and microhardness analysis were conducted. The results indicate that the best mechanical properties, including yield strength and ultimate tensile strength, were observed in the interface between the fourth and fifth layers. Compared to the interface between the first and second layers the yield strength and ultimate tensile strength increased by 55.41 % and 48.61 %, respectively. The microstructural characteristics of the FSAM process reveal that the upper layers exhibit a finer grain structure. However, T6 heat treatment leads to the formation of continued Grain Growth (CGG) and Abnormal Grain Growth (AGG), which significantly reduces the mechanical properties of the material
  9. Keywords:
  10. Friction Stir Welding ; Additive Manufacturing ; Aluminum Alloy 6061 ; Structure-Property Relationship ; Friction Stir Additive Manufacturing

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