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Semi-Solid Forming of AZ91 Magnesium Alloy by using Electromagnetic Stirring

Farzam Mehr, Navid | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46596 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Aashuri, Hossein
  7. Abstract:
  8. In the last decade, magnesium alloy has been developed owing to it’s low density, high specific strength, good castability and damping property. AZ91 alloy is proved to be the most common and most important magnesium casting alloy. It is shown that, rheocasting process is a proper way which increases the mechanical properties of the products. Since 28 years, so many new methods for preparing Semi-Solid alloy slurry and rheoforming process have been suggested. Electromagnetic Stirring ( EMS ) method was used for making globular structures. In this research, the semi-solid slurry of AZ91 magnesium alloy was prepared by electromagnetic stirrer under different conditions of stirring current and stirring time. Ca was added to the melt for ignition proof effects. The prepared semi-solid slurry, was injected into a step-die cavity with 5,7 and 9 millimeter thickness and the influence of thickness of steps, stirring current and stirring time, on shape factor, equivalent globules diameter and liquid fraction were investigated. Experimental results showed that if the stirring current increases, the dendritic microstructure will transform to rosette shape and round primary-Mg phase particles and distributing it into the eutectic phase. The optimum conditions of electromagnetic stirring was obtained with stirring under 55 (A) current, 30 (S) stirring time. The amount of shape factor in this conditions, was 0.84. By increasing the thickness of steps, the shape factor decreased. In the rheocasting process, it is shown that liquid segregation is avoided when high injection speed, is applied. The influence of thickness of steps, on micro hardness was also investigated. According to the results, by decreasing the thickness of steps, the micro hardness will increase
  9. Keywords:
  10. Electromagnetic Stirrer ; Globular Microstructure ; Aluminum-Magnesium Alloy ; Step-Die ; Semi-Solid Processing ; Rheocasting

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