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The Effect of Rolling on the Mechanical Properties and Microstructure of Al 1050 Sheet Joined with Friction stir Welding

Zinatlou Ajabshir, Sina | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49138 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Hossein kokabi, Amir; Kazeminezhad, Mohsen
  7. Abstract:
  8. One of the Friction Stir Welding (FSW) limitation is thinner sheets joining. To solve this limitation, sheets were welded through FSW at upper thickness and then reduced welded samples thickness. In this research, 3-mm-thick AA1050 aluminum plates were joined by FSW.For this purpose, the effect of welding parameters on microstructure and mechanical properties of the welded samples were investigated by changing the ratios of rotational speed (900,1200 rpm) to travel speed (50,90,150 mm/min) (ω/v). It was revealed that the grain growth rate was strongly increased with the increase of the heat input by rotational speed at constant travel speed. Subsequently, hardness reduction was observed in the stir zone at higher rotational speed compared with that at lower one. Stir Zone (SZ) grain size span measured 3.4-5.4µm. The effect of welding on the tensile properties and fracture was studied. It showed that welding reduced 13-29% the transverse Ultimate Tensile Strength (UTS) of the FSW samples unto Base Metal (BM). Also, it has been observed that the fracture location of tensile test specimens was placed at the SZ/thermomechanical affected zone (TMAZ) interface on the advancing side at lower travel speed, while at higher travel speed, it was placed at the heataffected zone (HAZ)/TMAZ interface on the retreating side.Then welded samples were rolled at different Cold Work (CW) percentage that samples thickness became 2mm and 1mm. This study aims to study the evolution of microstructure during post-rolling of FSW welded samples and its effect on the mechanical properties and fracture of the FSW joint. A detailed characterization of microstructure showed that postrolling increased Aspect Ratio (AR), grain boundry and dislocation density.The effect of post-rolling on the tensile properties and fracture was studied. It showed that postrolling increased the transverse UTS of the FSW samples unto BM, and the UTS was increased further with the increase of rolling strain. The UTS of sample (50 mm/min, 1200 rpm) was raised from ∼76MPa of the FSW-undeformed specimen to ∼124MPa for the FSW-CW-33% and ∼148MPa for the FSW-CW-66% specimens. Fracture occurred at BM/TMAZ interface for most the FSW-rolled specimens
  9. Keywords:
  10. Aluminum ; Friction Stir Welding ; Cold Rolling ; Microstructure ; Mechanical Properties ; Aluminum Alloy 1050

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