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Enhancing Corrosion Resistance of Plasma Electrolytic Oxidation Coating on 5052 Al Alloy By using TiO2 Nano Particles

Azimi, Amir Hossein | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58194 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ghorbani, Mohammad
  7. Abstract:
  8. Plasma electrolytic oxidation (PEO) is an advanced technique for creating composite/ceramic coatings on lightweight metals such as aluminum, magnesium, and titanium. This study aims to enhance the corrosion resistance of 5052 aluminum alloy by applying a PEO coating incorporating titanium dioxide (TiO₂) nanoparticles. Initially, samples were coated in a silicate-based electrolyte bath (containing 10 g/L sodium metasilicate and 2 g/L potassium hydroxide) at different processing times (5, 10, and 15 minutes) and current densities (0.2, 0.3, 0.4, and 0.5 A/cm²) to determine the optimal coating conditions. Once the optimal parameters were identified, TiO₂ nanoparticles were added to the electrolyte at concentrations of 0.25, 0.5, 0.75, and 1 g/L, and the coatings were applied accordingly.The phase composition of the coatings was analyzed using X-ray diffraction (XRD). The surface morphology and elemental composition were examined through field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS). SEM images revealed that the coatings exhibited a porous structure consisting of a dense inner layer and a porous outer layer. The corrosion behavior of the coatings was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The effect of processing time and current density on coating thickness was measured using an eddy current device and validated with optical microscopy results. Potentiodynamic polarization analysis showed that the corrosion current density of the uncoated aluminum alloy was 2.6×10−7.Applying a PEO coating under optimized conditions (0.4 A/cm² and 10 minutes) reduced the corrosion current density to 5.9×10−10. Further addition of 0.75 g/L TiO₂ nanoparticles reduced this value to 2.0×10−10. Nyquist plots were used to assess the resistance of the developed coatings, revealing that the coating resistance at 10 minutes and 0.4 A/cm² was 15×105, which increased to 28×105with the addition of 0.75 g/L TiO₂ nanoparticles. This improvement is attributed to the formation of a corrosion-resistant layer on the alloy surface, which initially contained multiple pores. The addition of nanoparticles reduced micro discharges, resulting in smaller pore sizes and a denser surface layer. Finally, the coating hardness was examined, showing an increase from 60 Vickers (for the uncoated alloy) to 92 Vickers for the nanoparticle-free coating (processed for 10 minutes). The hardness further increased to 166 Vickers for coatings produced in an electrolyte containing 0.75 g/L TiO₂ nanoparticles
  9. Keywords:
  10. Plasma Electrolytic Oxidation ; Corrosion Resistance ; Titanium Dioxide Nanoparticles ; Alumina/Titanium Dioxide Composite Coating ; Corrosion Resistance ; Aluminum Alloy 5052

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