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Effects of Oxide Film on Tensile Properties of A356 Aluminium Alloys

Mousavi, Fariba | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43868 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Davami, Parviz; Varahram, Nasser
  7. Abstract:
  8. Since mechanical properties of cast Al-Si-Mg alloys are directly influenced by microstructural defects, understanding the characteristics of these defects and any interaction between them is important for improving the properties of castings. This study investigated the effect of the most common defects normally found in cast aluminium alloys namely, double oxide films, Fe-rich phases and prosity. A different level of each defect was introduced into castings to investigate their effects on tensile properties of A356 Alloy. Differents casting condition experiment produced different entrained oxide film, Fe-rich phases and porosity caused by shrinkage content, from low to high, were tested using tensile test bars that were cast in a CO2 sand mould. icrostructure and fracture surface of samples were examined by optical microscopy, SEM and EDX.Results showed that the most important defect in this research was oxide film that had an effect on UTS, σy and elongation of about 17 MPa, 39 MPa and 1.33% respectively.
    Increasing Fe content from 0.1 to 0.5wt% influenced the tensile properties of the castings by decreasing the UTS, σy and elongation by about 43MPa, 63 MPa and 1.52%respectively.
    The most important imteraction found in this research was the interaction between oxide film and porosity suggesting a mechanism for porosity formation in which entrained oxide film acted as initiation sites for pore formation in the casting. The main factor in the formation of prosity was hydrogen and shrinkage, since both could encourage the expansion of oxide film defects to become gas porosity or shrinkage porosity in the castings. The other interaction between the microstructural defects observed in this research was that oxide films were found to be substrates for the nucleation and growth of Fe-rich phases, particularly the β-Al5FeSi phase. An interaction between all three defects were also observed
  9. Keywords:
  10. Aluminum Alloy A356 ; Tensile Strength ; Porosity ; Oxide Films ; Ferrous Rich Phases

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