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Formation of Plasma Electrolytic Oxidation Coating on Mg-Ti Coupl Joint with Friction stir Welding Process and Evaluation its Properties

Aliabadi, Ali | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48338 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ghorbani, Mohammad
  7. Abstract:
  8. Plasma electrolytic oxidation is the novel surface engineering technology that used as the low cost and eco-friendly method for improvement of corrosion resistance and wear resistance of Mg and Ti alloys. The aim of this investigation is firstly joint the Ti and Mg, then optimization of coating process condition of Ti-Mg couple for achieve the best corrosion and wear resistance of coating. For this purpose, initially Ti and Mg were joint together by friction stir welding treatment and then the effect of coating variable such as type of electrolyte, coating voltage, coating time and the concentration of the bath constitute, on the coating properties were investigated, and then the effect of coating stage on coating properties were studied. Scanning electron microscopy, X-ray diffraction and potentiodynamic polarization methods were used for evaluation of morphology and microstructure, phase content and corrosion resistance respectively. The results of this investigation indicated that, the optimized condition of silicate base electrolyte are: silicate concentration=10g/L, coating process time= 15 min and coating voltage= 260 V in which the corrosion current density of the coating formed on Mg was equal to 5.8µA/cm2 and equal to 2.5 µA/cm2 for the coating formed on Ti. The optimized condition for the aluminate base electrolyte are: aluminate concentration= 10g/L, coating process time=15 min and the coating voltage= 290 V, in which, corrosion current density of the coating formed on Mg was calculated equal to 0.9µA/cm2 and equal to 1.7 µA/cm2 for the coating formed on Ti. The coating thickness in the mentioned optimized condition was equal to 9.1µm at the coating formed on Mg and equal to 13.4 µm at the coating formed on Ti in the silicate solution and measured equal to 4.7µm at the coating formed on Mg and equal to 14.5 µm at the coating formed on Ti in the aluminate solution. Also the results showed that, in two steps coating treatment compared with the one step treatment, the coating thickness was increased and the corrosion resistance was increased. Finally, the best corrosion and wear resistance was obtained in the coating formed in two steps coating treatment firstly in silicate base and then in the aluminate base electrolyte in the 20 min. in which condition the corrosion current density of the coating formed in Mg was equal to 0.6 µA/cm2 and equal to 0.4 µA/cm2 for the coating formed on Ti. The coating thickness for this condition was equal to 17.4µm for Mg and 24.2 µm for Ti. Also in this condition the wear rate reduced from 2.8*10-5 to 1.52*10-6 g/N for Mg and from 8.43*10-6 to 7.88*10-7g/N for Ti
  9. Keywords:
  10. Friction Stir Welding ; AZ31 Magnesium Alloy ; Titanium ; Plasma Electrolytic Oxidation

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