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An Investigation into the Effect Of Severe Plastic Deformation by Equal Channel Angular Extrusion (Ecae) Process on Mechanical and Microstructural Properties of a Mg-Zn Alloy

Shaeri, Morteza | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 46771 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Karimi Taheri, Ali
  7. Abstract:
  8. The specific properties of some of magnesium alloys have caused these alloys to be used in medical and industrial applications. Adding new elements and applying severe plastic deformation to these alloys have been considered as a clue for improving their mechanical properties. The aim of this project is to improve the mechanical properties of a magnesium alloy by using new alloying elements and applying the ECAP process.
    In this project, a new magnesium alloy by composition of Mg-1.78Zn-0.72Si-0.41Ca was cast. After casting, solution treating and annealing of the alloy were studied. Then, the effect of ECAP process on microstructure and mechanical properties of the annealed and solution treated alloy at 300 ᵒC, 350 ᵒC and 400 ᵒC was investigated. Finally, the aging of the solution treated alloy, before, during and after ECAP was assessed. The temperature and time of quench aging were in the range of 125 to 200 ᵒC and 0 to 24 h respectively. The aging of ECAPed specimens was carried out at 125 ᵒC and 150 ᵒC for the times up to 24 h. the mechanical properties, phase transformation and microstructure of the ECAPed and aged samples were evaluated using hardness, shear punch test, OM, FEGSEM, DSC and XRD tests. The results showed that the suitable time and temperature for both annealing and solution treating of the alloy are 8 h and 500 ᵒC, respectively. The annealed samples were ECAPed successfully at 300 ᵒC but the solution treated samples were failed at this temperature. But solution treated samples were successfully ECAPed at 350 ᵒC and 400 ᵒC. the ECAP process at 350 ᵒC for 4 passes greatly improved the mechanical properties and decreased the grain size to 2.5 μm while ECAP at 400 ᵒC was not much effective. The results suggested that aging for 16 h at 150 ᵒC is the optimum aging condition for the solution treated samples. During the first pass of ECAP at 350 ᵒC dynamic aging occurred and the aging process after ECAP couldn’t enhance the mechanical properties
  9. Keywords:
  10. Microstructure ; Mechanical Properties ; Age Hardening ; Equal Channel Angular Pressing (ECAP) ; Magnesium Alloy with Silicon and Calcium

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