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The Effect of Rolling on the Mechanical Properties and Microstructure of Dissimilar Friction Stir Welded AA1050 – AA6082-T6 Sheets

Hoseyni, Sajad | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44622 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kokabi, Amir Hossein; Kazeminezhad, Mohsen
  7. Abstract:
  8. One of the limitations of friction stir welding process is joining of sheets with low thickness. Interference ways for these limitations are joint in higher thicknesses and thickness reduction in included joint samples. In this study, in the first process, with the optimization of the variables affecting the process, joint was performed using visual inspection, mechanical properties and micro structural studies. In the next process, using the rolling operation for the reduction percent of different thicknesses, the most appropriate route was chosen. 1050 aluminum sheets (1050 and 6082-T6) with a thickness of 3 mm were welded using friction stir welding in tool rotary speeds of 1200 and 800 rpm and feed of 90 and 150 mm / min. Joints were made with a diameter of shoulder 15 mm, pin 5mm and the length of pin 2.8 mm in both manners of similar and dissimilar. Then, using the cold rolling operation in reduction percent of thicknesses 33 and 66, thicknesses of welded sheet were decreased to 2 and 1 mm, respectively. Finally, to investigate the mechanical properties and microstructure of welded sheets, the effect of the cold-rolling was studied on the joint of sheets. Findings revealed that noted sheets in different situations of welding included an appropriate weldability in both similar and dissimilar. In addition, the best joint in dissimilar metals was performed in tool rotational speeds of 800rpm and the feed rate of 15mm/min and by setting aluminium alloy 1050 in retreating side. so that in dissimilar joint, with reduction of rotational speeds to feed rate ratio from 13.33 to 5.33, the grain size in the nugget and heat affected zones in retreating side Decreased 35.4% and 39.9%, Respectively and in advancing side Decreased 7.3% and 31.7%, Respectively; moreover the tensile strength improvement was 9%. Reduction percent in the thickness of cold rolled sheets joined by FSW process did not cause to destroy the joint and separate the connection between nugget zone and base metal. Moreover, after cold rolling, the form of the grains in different places of joint changed from equiaxed to elongated smaller ones; also the hardness and tensile strength of joint increased so that the ultimate tensile strength of the best dissimilar joint rolled by 33% was about 0.5% higher than the tensile strength of 1050 aluminum sheets. In addition, the place of fracture in the tensile test was transferred to the base metal
  9. Keywords:
  10. Cold Rolling ; Microstructure ; Mechanical Properties ; Aluminum ; Friction Stir Welding

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