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Friction Stir Welding of 3000 Series Aluminum Alloy by Adding Cu Powder

Abnar, Behrouz | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44605 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kokabi, Amir Hossein; Kazeminezhad, Mohsen
  7. Abstract:
  8. An increase in strength of friction stir welded (FSW) AA3003-H18 sheets is important, due to the reduction of mechanical properties in weld area such as heat affected zone and stir zone during welding. In this research, at first FSW was used to join 3003-H18 non-heat-treatable aluminum plates without adding copper powder. The specimens were joined at various rotational speeds (800, 1000 and 1200 rpm) and traverse speeds (40, 70 and 100 mm/min). In these cases, the effects of welding parameters on microstructure and mechanical properties were investigated. The average grain size of stir zone was in the range of 21.7-7.8 μm and the microhardness of them was 28-37 Hv. Then FSW was used to join AA3003-H18 plates by adding copper powder. The copper powder was first added to the gap between two plates and then the FSW was performed. The specimens were joined at various rotational speeds of 800, 1000 and 1200 rpm at a constant traveling speed of 100 mm/min. In the last, this processing was used to join AA3003-H18 plates by adding mixture of pure aluminum and copper powder. The effects of rotational speed, number of FSW passes and direction of second pass were studied on copper particle distribution and formation of intermetallic compounds in the microstructure. The second pass of FSW was carried out in both the same (2 forward passes) and the reverse directions (2 forward-backward passes) of the first pass. In addition, the effect of powder compaction on copper clusters was evaluated. The mechanical properties and microstructures were investigated. The copper particle distribution and percent of Al-Cu intermetallic compounds were increased with increasing the rotational speed and number of passes. Al2Cu and AlCu intermetallic phases were formed in the stir zone and consequently the hardness was significantly increased. The copper particles and the generated in situ intermetallic compounds were symmetrically distributed in both advancing and retreating sides of weld zone after 2 forward-backward passes and the wider area was reinforced by the intermetallic compounds. Also, the tensile test specimens tend to fracture from the coarse copper aggregation at the low rotational speeds. At high rotational speeds, the fracture locations are placed in HAZ and TMAZ. When the pure copper powder was used, the copper cluster size was in the range of 4.9- 117.8 μm. On the other hand it was in the range of 5- 25.4 μm, when mixture of aluminum and copper powder was used. Also, the copper particles and hardness distributions in using mixture of aluminum and copper powder were improved
  9. Keywords:
  10. Aluminum Alloy Series 3xxx ; Microstructure ; Mechanical Properties ; Friction Stir Welding ; Copper Powder

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