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Prediction of Weld Solidification Cracking Susceptibility in Dissimilar Aluminium Alloy Joints

Bodaghi, Fatemeh | 2024

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 57300 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kokabi, Amir Hossein; Movahhedi, Mojtaba; Tavakkoli, Rouhollah
  7. Abstract:
  8. Solidification cracking is one of the most common types of cracks in aluminum alloy welds. Predicting the possibility of Solidification cracking can be useful in selecting the variables of the welding process in such a way that a crack-free joint is obtained. In the present research, in the first stage, a criterion of sensitivity to solidification cracking is presented by considering the anisotropic permeability equation and direction of applying deformation to the melt pool. Then, the criterion has been investigated for aluminum-copper and aluminum-copper-silicon alloys. The results indicated that Al-3.5 wt% Cu alloy has the highest solidification cracking susceptibility (SCS) in the brittle temperature range of these alloys. In addition, alloys with low silica and high copper are the most sensitive alloys. Solidification cracking criteria require data such as temperature gradient and changes of solid fraction with temperature, which are dependent on the chemical composition of the weld pool, as inputs. These cases in a welding pool, especially dissimilar welding, are affected by welding process variables. Therefore, in this research, a welding simulation was used for dissimilar joints of 2024, 5083 and 6061aluminum alloys with 1070, 5183 and 4043 aluminum filler alloys. For this purpose, Flow 3D software based on finite volume method was used. Using video recording of the arc during welding and Abel's inversion method, the arc characteristics were determined and the necessary subprograms were written. Further, by completing the simulation, its outputs such as temperature gradient, isotherm velocities, weld metal composition and properties were determined and used as the input of solidification cracking susceptibility criterion. In order to confirm the simulation results and the SCS model, the weldability test was performed for similar alloys and welding conditions. Based on the weldability test, the normal crack length values for joining 2024 and 6061 sheets using 5183 and 1070 filler metal were obtained as 0.729 and 1, respectively. For the joining of 5083 and 6061 sheets, the value of the normal crack length for the welded sample using 5183 and 1070 filler metal was obtained as 0.922 and 0.898, respectively. The length of the interdendritic melt channel in joining 2024 and 6061 aluminum sheets with 5183 aluminum filler metal increased from 0.5 mm at 145 A to 1.22 mm at 175 A. Also, with the increase in welding speed, the velocity of isotherms (Vt) increased from 1.3 mm/s at a speed of 18 cm/min to 2.4 mm/s at a speed of 24 cm/min. According to the model, increasing the length of liquid channel and the velocity of the isotherms has led to an increase in SCS with an increase in the welding current and speed. In general, the model results are in good agreement with the weldability test results. Investigation of weldability of joints with the model and weldability test confirmed that the 4043 filler metal produced the lowest SCS. In addition, the weld joint of 2024 and 6061 aluminum sheets is more prone to solidification cracking than the joint of 5083 and 6061 aluminum sheets. Therefore, it can be concluded that by using the simulation and accurate determination of SCS model parameters instead of using the same hypothetical values for different samples, a more accurate prediction of the solidification cracking susceptibility of joints will be obtained
  9. Keywords:
  10. Free Surface Modeling ; Aluminum Alloy ; Weldability ; Dissimilar Joint ; Melt Flow Simulation in Welds ; Solidification Cracking Modeling ; Solidification Cracking Susceptibility

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