Corrosão da liga A380 anodizada por oxidação a plasma eletrolítico aplicando degraus temporais de tensão

Abstract

A380 alloys are widely used in various applications due to their mechanical properties, but still require surface treatments such as anodization. However, anodizing highsilicon alloys can be a challenging and costly process due to the formation of a lowelectrical-conductivity oxide layer and the duration of the process, the latter being responsible for the high energy consumption and the extensive use of compounds in the electrochemical bath. Electrolytic plasma is a promising alternative to anodization as it helps achieve a surface with better corrosion resistance and more uniform surface finish. This study aimed to evaluate the corrosion and the phases present in the microstructure produced by the PEO (Plasma Electrolytic Oxidation) treatment combined with the Step Method application. The samples were subjected to stepwise voltages from 0 to 420V under also stepwise times of 120 seconds, reaching final times of 480 and 600 seconds for the formation of the protective layer. Subsequently, the modified surface data were evaluated by profilometry, with 30-second measurements for each region. Scanning electron microscope (SEM) images were obtained operating at 20kV, and X-ray diffraction spectra were obtained from Bragg configuration with a step size fixed at 0.02° and an interval ranging from 15° to 90°. The results showed that the application of pre-voltage during the process improved the roughness (with the best result of Ra = 5.58 ± 0.40μm) and the surface finish of the samples. The formation of pure aluminum and silicon oxides from the sample matrix was observed along with the formation of gamma alumina (γ-Al2O3) and mullite, the latter phase resulting from the interaction of aluminum and silicon oxides together. The samples where moderate voltages were applied showed the best polarization curve results, with corrosion potential values of -0.665mV for treatment (T3) and -0.680mV for treatment 4 (T4). The results suggest that electrolytic plasma with pre-voltage is a promising alternative to anodizing for A380 alloys. The method improves corrosion resistance and the roughness of the samples.