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Formation of Globular Microstructure by Electromagnetic Stirring and Rheocasting of Semi-Solid A356 Aluminum Alloy

Asadi Khanouki, Mohammad Taghi | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41198 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ashuri, Hossein
  7. Abstract:
  8. The study on new rheoforming technologies of semi-solid alloys has recently been one main subject interesting many researchers and industrials, and so many new methods about preparing semi-solid alloy slurry and rheoforming process have been suggested. Among more than 20 proposed methods, only MHD (Magneto Hydro Dynamics) and EMS (electromagnetic stirring) methods has been industrialized. In this research, the semi-solid slurry of A356 aluminum alloy was fabricated by electromagnetic stirrer under different conditions of stirring current, stirring time and pouring temperatures. Then the semi-solid slurry prepared in optimum conditions was injected into a step-die cavity by a drop device and the influence of preheating temperature and thickness of steps on filling behavior was investigated. In order to investigate the distribution of electromagnetic fields and its influence on globularity of A356 Aluminum alloy microstructure, electromagnetic fields was analyzed by Maxwell simulation software. The simulation results showed that the maximum intensity of magnetic flux density occurs in bottom of crucible and near the coils. It was noticed that increase in ampere-turns, intensify the magnetic field in the semi-solid slurry. Experimental results showed that if the magnetic flux density and stirring time increased and pouring temperature decreased, the dendritic microstructure transformed to rosette shape and spherical primary-Al phase particles and distributing it into the eutectic phase. The optimum conditions of electromagnetic stirring was obtained with stirring under 70A current, 0.09T maximum magnetic field intensity, 60s stirring time and pouring temperature of 650℃. In rheocasting process, it is determined that high injection speed prevented from the liquid segregation. Also, when the preheating temperature of step-die increased, thin steps was filled easily but mechanical properties of alloy was decreased
  9. Keywords:
  10. Semi-Solid Processing ; Electromagnetic Stirrer ; Globular Microstructure ; Aluminum Alloy A356 ; Rheocasting ; Step-Die

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