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Semisolid Stir Joining of AZ91 Alloy to A356 Alloy

Harati, Meysam | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48556 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ashuri, Hossein
  7. Abstract:
  8. Today, Mg and Al as the widely used metals, make a special contribution to automotive, electronics and aerospace industries. Increasing the application of alloys of these metals, has extended the demand for reliable joint between alloys of these two metals. The main problem with the dissimilar joining of A356 alloy and AZ91 alloy is hard and brittle intermetallic compounds formation such as Mg17Al12 and Mg2Si which brings about welding strength reduction. By far, a large number of researches about dissimilar joining of AZ91 alloy and A356 alloy in semi-solid condition have not accomplished. In this method two fragments, one from AZ91 alloy and another from A356 alloy among which was a 2 millimeter Zn-%3Ni intermediate layer, were heated up to specified temperatures (555, 560 and 570 Celsius). Then this region was stirred with a drilling form instrument by three different speed (500, 875 and 1250 rpm) and finally was cooled in oil. During another experiment, joining was performed with the Cu refrigerant besides AZ91 alloy in order to set two alloys in semi-solid region. A noticeable point was that joining was operated with only a little sulfur, without any protective gas. Joints were investigated in terms of macro structure, micro structure and mechanical, and three joint regions were identified. In addition, it was observed that a wide range of phases containing Mg-Al-Zn-Si were formed in different parts of joint. The ultimate shear strength (shear punch experiment) reached 89 percent of A356 base metal and 73 percent of AZ91 base metal. By modification of the experiment with Cu refrigerant, ultimate shear strength was achieved until 92 percent of A356 base metal and 76 percent of AZ91 base metal, eventually
  9. Keywords:
  10. Semisolid Joining ; Interlayer ; Aluminum Alloy A356 ; Shear Punch Test ; AZ91 Magnesium Alloy ; Speed Joining

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