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Investigation on Pulsed TIG Lap Welding of Al-5052 Sheet to Al-1050 Clad St-12 Sheet

Hassanniah, Abbas | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49970 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Movahhedi, Mojtaba
  7. Abstract:
  8. In this study, Al-5052 aluminium alloy sheet was lap joined to aluminium clad steel sheet using pulsed gas tungsten arc welding and Al-Si filler metal. Effect of heat-input, thickness of clad layer and frequency were investigated on the formation of intermetallic reaction layer, microstructure of the weld seam and shear strength of the joints are explored. Stress analysis in weld is also used in order to justify the fracture location in the welds the microstructure and shear-tensile strength of the welds (joining with A1-1050 clad layer with two thickness of 350 μm and 1000 μm). Before welding, aluminum clad steel sheets were produced by roll bonding and 450 °C annealing temperature and 90 min annealing time. Results shows that joining mechanism is changed with the change of the thickness of the Al-1050 interlayer. During welding, the interlayer with a thickness of 1000 μm is partially melted and the join between the base metal Al-5052 and A1-1050 interlayer was performed by the fusion welding mechanism. While, the interlayer with a thickness of 350 μm is completely melted and the molten of the filler metal is contacted with St-12. In this case, the joint between the base metal Al-5052 and St-12 was performed by the welding-brazing mechanism. Primary dendrite arm spacing in the weld metal and the average reaction layer thickness formed at the interface of the deposited filler metal and the St-12 base steel increased with enhancement of the weld heat-input. However, formation of intermetallic layer with the thickness less than ~3 µm was not detrimental for the joint strength. At weld with an Al-1050 interlayer thickness of 1000 μm, the shear-tensile strength of the weld linearly reduced by increasing the input heat. The primary α-Al dendrite arm spacing increased with enhancement of heat-input since at a higher heat-input, the maximum temperature experienced by the weld metal increases and the cooling rate decreases. But at weld with an Al-1050 interlayer thickness of 350 μm, shear-tensile strength of the joints first increased by enhancement of the heat-input up to 250 J.mm-1 and then decreased with further increase in the heat-input. The first increasing trend of the joint strength was due to the improvement in the wetting and bonding between the weld metal and the aluminium clad layer in the weld root with raising the heat-input. However, the decreasing trend of the joint strength beyond the optimum heat-input was attributed to the reduction in the strength of the deposited filler metal with higher primary dendrite arm spacing. At the optimum weld heat-input, the joint strength reached to ~90% of the Al-5052-H34 base metal strength. Fracture path in all the welds had an angle of ~75 with respect to the horizontal base plane. Stress analysis in the weld showed that fracture in the joint was controlled mainly by the maximum normal stress component of the imposed stress during shear-tensile test
  9. Keywords:
  10. Roll Bonding ; Heat Input ; Gas Tungsten Arc Welding (GTAW) ; Pulse Current ; Aluminum Alloy 5052 ; Aluminum Clad Steel Sheet ; Tensile-shear Strength

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