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Effect of Interlayer Prepared by Plasma Electrolytic Oxidation in Joint of Ti6Al4V and Al6061-t6 by Friction Stir Welding

Iravani, Parniya | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56771 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ghorbani, Mohammad
  7. Abstract:
  8. Connecting titanium and aluminum alloys is widely used in different industries such as transportation, chemical, aircraft manufacturing, etc. Friction stir welding is one of the methods of joining these two metals. In order to obtain a sound joint, the formation of intermetallic phases in the interface must be controlled. One of the ways to control these phases is the use of an interlayer, which in this research is the interlayer applied by plasma electrolytic oxidation method with different current densities and coating times. In this regards, first the optimal parameters of friction stir welding were determined. Then, Ti6Al4V and Al6061-t6 welding was performed in the presence of interlayers prepared with the current densities of 250 to 450 mA/cm2 and with a duration of 270 to 1080 seconds. Microscopic investigations, shear tensile and polarization tests and X-ray diffraction analysis were performed to investigate the effect of coating properties on the joint. Also, thickness and size of the pores in each coatings were measured. It can be observed that the interlayer of plasma electrolytic oxidation reduces the intermetallic compounds by decreasing the reaction time of titanium and aluminum which leads to increase the shear strength and reduce the corrosion rate of the samples. In the presence of the interlayer carried out at a current density of 250 mA/cm2 for 540 seconds, the highest strength of 173.8 MPa were obtained. Increasing the current density and coating time lead to an increase in thickness and porosity of interlayers, which first increase and then decrease the joint properties. In the presence of interlayers applied at current density of 450 mA/cm2 and the interlayer carried out for 1080 seconds, the strength was 74.54 and 75.10 MPa, respectively, which is lower than the welding strength without an interlayer of 88/66 MPa. The corrosion rate of welds in the presence of the interlayer is lower than the weld without this layer because the intermetallic compounds act as microcathodes and their reduction reduces the corrosion rate. In the presence of the interlayer, the corrosion rate decreased from 3.03×10-6 A/cm2 for welding without these layers, to even lower values up to 1.73×10-6 A/cm2 for the C250T540 interlayer. In comparison with the interlayers, in the layers applied with high thickness and porosity, large oxide particles lead to an increase in the corrosion rate until in the presence of C450T540 and C250T1080 interlayers, the corrosion rate increased to 65.2×10-6 and 2.83×10-6 A/cm2
  9. Keywords:
  10. Aluminum ; Titanium ; Friction Stir Welding ; Interlayer ; Plasma Electrolytic Oxidation ; Titanium Alloy ; Aluminum Alloy 6061

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