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Investigation of the Effects of Oxide films on the Mechanical Properties of Al-A356.2 alloy and Simulation of Oxide film Entrapment during the Mold Filling

Eisaabadi Bozchaloei, Ghasem | 2013

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 44266 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Davami, Parviz; Varahram, Naser
  7. Abstract:
  8. The present study aimed to investigate the effects of old and young oxide films on the mechanical properties and reliability of Cast Al A356.2 alloy. The results indicate that the presence of oxides within the microstructure of the alloy decreased the tensile properties of the alloy and increased their scattering. Beside this, the presence of the oxides decreased the reliability of the alloy. The results showed that the presence of double oxide films (especially old oxides) decreased the Weibull modulus of tensile properties and resulted in bi-Weibull distribution in tensile properties of the alloy. The results also indicate that using of a clean melt (with high quality), is vital for production of castings with high reliability. Also, it was shown that the damage done to the liquid metal is at best only partially mitigated by the filter, and at worst, remains permanent despite the use of a filter. From the results of Weibull analysis, it was found that the use of a 10 ppi filter to be 72% effective in catching the coarse old bifilms. Also, the results clearly showed that besides the high quality of the melt, the design of the gating system, plays an important role in determination of the reliability of the castings. The investigation of the effects of runner height after filter in naturally pressurized running system showed that with increasing the falling height of the melt (runner height after filter) beyond a critical height, a large number of double oxide films will be entrapped within the bulk of the liquid metal, which in turn, results in degradation of the reliability of the castings. A noble method has been proposed for removal of dissolved hydrogen and double oxide film from Al melt, based on the re-melting of the alloy. The results showed that remelting of the alloy inside the crucible is an effective method for increasing the melt quality. Forthermore, it was shown that remelting inside the crucible increased the UTS and El% of the alloy by 19 and 97%, respectively. A simple algorithm has been proposed for simulation of the entrapment of double oxide films during the mold filling of the Al castings. Comparison of the results obtained from simulation and the experiment showed that the proposed model could predict the entrapment o double oxide films and their final position in castings with acceptable accuracy
  9. Keywords:
  10. Simulation ; Oxide Films ; Weible Model ; Tensile Properties ; Reliability ; Aluminum-Silicon-Magnesium Alloy

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