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Enhancement of the Corrosion Resistance and Surface Tribology of Plasma Electrolytic Oxidation Coating on Aluminium 5052 alloy via Addition of Zirconia Nanoparticles

Bahojb Khoshnoudi, Elshan | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57734 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ghorbani, Mohammad
  7. Abstract:
  8. Developing ceramic coatings using Plasma Electrolytic Oxidation is a common method for improving the corrosion resistance of Aluminum alloys. However, by changing the process parameters and modification the coating, the properties of the obtained coating can be changed. For this purpose, the effect of current density and applied coating time on corrosion resistance, microstructure and hardness of the coating was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy, microhardness, phase analysis (XRD) and microstructural analysis (SEM). In order to investigate the effect of current density, 5052 aluminum samples were coated in the range of 20-40 A/dm2 for 5 minutes. The results showed that the sample coated with a current density of 25 A/dm2 showed the best corrosion current density of 2.97×10-7 A/cm2 with an average pore size of 1.0 microns and the dominant phase was γ-Al2O3. With increasing current density, structural defects such as cracks and enlargement of pores up to 1.2 microns were observed. Also, to investigate the effect of time, the samples were coated with a current density of 25 A/dm2 at different times of 2.5, 5, 7.5 and 10 minutes. By examining the coating application time in this time interval, within 10 minutes, the corrosion resistance decreased to 3.04×10-9  A/cm2 and the dominant phase was γ-Al2O3. It was observed that with increasing time from 5 to 7.5 and to 10 minutes, the size of the pores initially increased locally (from 1.2 to 1.67 microns) and then, the pores were gradually closed. Moreover, with increasing coating time, the number of defects in the coating increased. In both sections of the current density and time investigation, the EIS technique was used to measure the resistance and capacitance of the dense inner layer and the porous outer layer of the coating. To study the effect of Zirconia nanoparticles (with a particle size of 50-60 nm and spherical shape), different concentrations of 0, 0.25, 0.5, 0.75 and 1 g/l of nanometeric Zirconia were used as bath additive, and the samples were coated with the mentioned Zirconia concentrations at a constant current density of 25 A/dm2 and a time of 5 minutes. The effect of the presence of nanoparticles was studied using polarization, electrochemical impedance spectroscopy, microhardness, AFM, SEM and GIXRD tests. It was concluded that at higher concentrations, the agglomeration of nanoparticles led to a decrease in corrosion resistance, but the addition of Zirconia nanoparticles at a concentration of 0.25 g/L reduced the pore size (0.49 microns) and improved the corrosion resistance to the extent of 5.90×10-10 A/cm2. This composite coating, which contained monoclinic Zirconia and gamma Alumina, in addition to improving the corrosion resistance by reducing the surface roughness by up to 30 nm (from 233 to 201 nm) and increasing the hardness by 58% compared to the coated sample without additives, did also improve the surface quality and showed that it has a high potential in improving the properties of the plasma electrolytic oxidation coating on Aluminum 5052 alloy
  9. Keywords:
  10. Plasma Electrolytic Oxidation ; Aluminum Alloy 5052 ; Zirconia Nanoparticles ; Corrosion Resistance ; Microhardness ; Ceramic Coating

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