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Semisolid Stir Joining of AZ91 Magnesium alloy

Abbas Hosseini Niaraki, Vahid | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43563 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Aashuri, Hosseini
  7. Abstract:
  8. AZ91 is the most applicable alloy of magnesium alloys.Semisolid stir welding of AZ91 magnesium alloy was investigated due to its welding problem such oxide formation, hot cracking in weld metal, and high residual stress through solidification with special focus on the effect of the welding temperatures, stirring rates, and tool shape. The interlayer with thickness of 2mm was located between two AZ91 pieces with 7.5mm thickness. Then, they were heated to the desired temperatures (515C, 530C and 540C), the semisolid temperature of both base metal and interlayer. A grooved stirrer with six rotational speeds from 0rpm to 2000rpm was introduced into the stir weld seam and the welded coupons were cooled in air. At the optimum temperature, tests were redone with un-grooved stirrer and the welded samples were quenched in water. For each welding process, 5 g sulfur was putinto the hot plate to protect the system from oxidation. Optical microscopic and SEM investigation, microhardness test, shear punch test (SPT), and three points bending test were carried out to assess the joint properties. No bonding was observed, while the stirring was not applied. A wide range of Mg-Zn and Mg-Zn-Al phases were detected in the joint. Shear punch test of the joint shows 94 pct of ultimate shear stress of the base metal when the grooved stirrer was used, while the bending strength of the joint was only 67 pct of the bending strength of the base metal. The bending stress of joint reached to the bending strength of base metal when the simple stirrer was used and welded coupons were quenched in water. The globule diameter also reached to 30µm.
  9. Keywords:
  10. Interlayer ; Bend Test ; AZ91 Magnesium Alloy ; Semisolid Joining ; Weld Seam Stirring ; Stirrer Shape ; Stirrer Rotational Speed ; Three Point Bending Test

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