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Investigation of Mechanical Properties of Thixoformed Melt-Spin Al-30Si-5Fe Alloy

shafizadeh, Mahdi | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45411 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ashuri, Hossein; Varahram, Naser
  7. Abstract:
  8. Aluminum alloys are one of the most economical light alloys that are used in automobile and aerospace industries. Application of Al-Si alloys are considerably used more than other Al alloys. Hypereutectic Al-Si alloys are well developed among Al-Si alloys due to their excellent properties such as high wear resistance and low thermal expansion coefficient. In these alloys formation of the primary silicon particles and hard intermetallic compounds in a ductile matrix provides a desirable wear properties. Coarsening of these particles in the structure of castings will reduce their mechanical properties. Moreover, oxidation of powders and difficulty in manufacturing complex parts in powder metallurgy make it difficult to produce parts from these alloys. Therefore, in order to make an desirable structure to improve mechanical properties, the Al-30Si-5Fe alloy melt spinned and used for thixoforming process. The melt spinned ribbons were pulverized by a ball-mill, then powder were consolidated for thixoforming process by hot pressing in an argon atmosphere. In the next step consolidated pieces put in an injection chamber, heated to the semisolid state, and then kept for a certain period of time. Finally by using a hydraulic press with the ram speed of approximately 1m/s, the slurries were injected to the dumbbell shaped mold. In order to evaluate and compare the effects of rapid solidification process, several casting samples were thixoformed. Results showed that all thixoformed samples were structurally modified, also the primary needle like silicon particles and the inter metallic compounds were inverted to the multifaceted structure. It was concluded that among the thixoformed specimens, melt spinned sample has better properties than the other ones. The melt spinned and thixoformed samples produced at 700oC with holding time of 5 minute have the best mechanical properties. It was found that the average size of the hard particles were reduced from 160μm to 13.5μm. The compression strength and the wear coefficient were increased from 450MPa to 525MPa and decreased to 0.27, respectively the wear coefficient during the wear test in cast sample started from 0.3, and finally reached
  9. Keywords:
  10. Mechanical Properties ; Melt Spinning ; Thixoforming ; Hypereutectic Aluminum-Silicon-Ferrite

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