Investigation of corrosion resistance and surface properties of AA7075 ve AZ91 alloys coated with ceramic materials

In this thesis; It is aimed to increase the corrosion resistance of AA7075 aluminum alloy and AZ91 Mg alloys, which are widely used in systems where lightness is important, in different environments and to improve the properties of the materials. For this purpose, AA7075 and AZ91 substrate materials were coated using the atmospheric plasma coating method. Before the coating process, surface preparation process was applied to the base materials in order to increase the coating quality. The coating materials selected for the study were TiO2 and Al2O3, which are among the most suitable coating materials for thermal spray coating methods. For the coating process, coating material ratios of 3% TiO2 + 97% Al2O3, 13% TiO2 + 87% Al2O3, 40% TiO2 + 60% Al2O3, 100% TiO2 and 100% Al2O3 were used. After the coating process, coating thicknesses were measured from the side section of the samples using an SEM scanning electron microscope. Microstructure examinations were carried out using scanning electron microscopy (SEM) to determine the structural characterization of the coatings. In addition, structural characterization and composition point analyzes of the coatings were performed using energy dispersive spectroscopy (EDS). Surface roughness values before and after coating were determined for each coating. Corrosion experiments were carried out to determine the corrosion behavior of the coated samples. A potentiostat/galvanostat device was used for corrosion experiments. Before the corrosion tests, a bakelite process was applied to the samples in order to isolate the substrate material from the corrosive environment. Bakelite samples were cleaned ultrasonically. Two different corrosive environments were used for the study: 3.5% NaCl and 0.3 M H2SO4. Thus, the corrosion behavior of the substrate materials was determined according to their usage areas. After corrosion experiments, corrosion potential (Ecorr), corrosion rate, corrosion current (Icorr), polarization resistance (Rp) values were determined for each sample group using current density-potential curves. With these determined values, potentiodynamic polarization curves (Tafel curves) were drawn for each coating ratio. In addition, in order to determine the structural changes after the corrosion experiment, the corroded samples were examined by SEM scanning electron microscope and energy dispersion spectroscopy (EDS) analysis was performed. When the corrosion rates of the coatings applied on AA7075 substrate material in 3.5% NaCl environment were evaluated, the highest corrosion rate was obtained in the uncoated sample and the lowest corrosion rate was obtained in the 100% Al2O3 coated sample. When the corrosion rates of the coatings applied on AA7075 substrate material in 0.3M H2SO4 environment were evaluated, the highest corrosion rate was obtained in the uncoated sample and the lowest corrosion rate was obtained in the 100% TiO2 coated samples. When the corrosion rates of the coatings applied on AA7075 substrate material were examined, it was determined that they suffered more corrosion in 3.5% NaCl solution than in 0.3 M H2SO4 solution. When the corrosion rates of the coatings applied on AZ91 substrate material in 3.5% NaCl environment were evaluated, the highest corrosion rate was obtained in the uncoated sample and the lowest corrosion rate was obtained in the 100% Al2O3 coated sample. It was determined that the behavior of the coatings applied on AZ91 substrate material in a 0.3 M H2SO4 corrosive environment was similar to the results obtained in 3.5% NaCl solution. When the corrosion results of the coatings applied on AZ91 substrate material in 3.5% NaCl and 0.3 M H2SO4 environments were examined, the corrosion potential (Ecorr) of the samples subjected to corrosion in 0.3 M H2SO4 environment was obtained higher than the samples subjected to corrosion in 3.5% NaCl environment.