Evaluation of Microstructure, Chemical Composition and Corrosion Resistance of Oxide Coating, Produced by Hard Anodizing in Oxalic Acid Electrolyte
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Article Type:
Research/Original Article (دارای رتبه معتبر)
Abstract:

Hard anodizing, as one of the methods to improve surface properties, has always been considered for aluminum.But the difficulty of controlling the temperature and the formation of an anodic aluminum oxide layer at the bottom of the pores are two important problems in this method. In this investigation, by designing an anodizing reactor, precise control of the coating conditions and the use of a mild anodizing (at 40 volts) prior to hard anodizing (at 130 volts), current density changes during the coating of 1100 aluminum alloy in an oxalic acid solution were studied. The current density-time curves and field emission scanning electron microscopy (FESEM) images showed an increase of current density and a transition from mild to hard anodizing, which was accompanied by an increase in interpore distance. The x-ray diffraction (XRD) results indicate a coating with an amorphous alumina structure. Energy dispersive spectroscopy (EDS) analysis also showed that the coating only contains oxygen and aluminum due to the formation of alumina. The results of the polarization test indicated a significant improvement in the alloy corrosion resistancewith the application of aluminum oxide layer. Anodizing at three temperatures of zero, 10 and 17 ℃ showed that increasing the temperature would increase the charge density and thickness of the oxide layer, but there was no significant effect on the interpore distance, pore diameter, the thickness of the barrier layer and the pore density, indicating that these parameters are independent of current density. However, due to more corrosive intensity of solution, the range of changes in these parameters increases. The porosity of the coating also increasesfrom 15.6% to 17.3%. By comparing the anodizing of pure aluminum and 1100 aluminum alloy , it was found that the presence of alloying elements would lead to a reduction in the coating arrangement
Language:
Persian
Published:
Iranian Journal of Surface Science and Engineering, Volume:14 Issue: 37, 2019
Pages:
53 to 69
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