| Aluminum and its alloys are low density material with high strength, which are easy to shape and has excellent performance of surface decoration. Aluminum and its alloys are widely used in construction, decoration, aviation and everyday life. However, the presence of low surface hardness, poor wear resistance and corrosion defects limited its scope of application. Thus, the surface treatment of aluminum and its alloys is necessary prior to use, which can improve the hardness, wear resistance and corrosion resistance of surface. Due to its simple and low cost, anodic oxidation became the most commonly used method of surface protection. A dense layer of oxide film was formed on the material surface after anodic oxidation, to some extent, this layers improve the corrosion resistance of aluminum and its alloys. According to the structure of anodic oxidation films, it can be divided into barrier layer and porous layer, the shape of pores of the porous anodic oxide film layer has a very important influence on its corrosion resistance.The conventional sulfuric acid anodizing method was used on5052aluminum alloy, the shape of the micropores of the porous anodic oxide film layer was changed with the anodic oxidation process parameters-Sulfuric acid concentration, electric current density, oxidation time; the shape of the micropores was observed by scanning probe microscope, the corrosion resistance of the different anodic oxide films in3.5%NaCl solution was tested by polarization curves and electrochemical impedance spectroscopy, the thickness and hardness of the film was tested; the influence of pore types on the sealed anodic oxide film was analyzed.The experimental results show that:the pore-shape was changed with the anodic oxidation process parameters, according to the shape of the pores, the anodic oxide film can be divided into three types of A. B. C;through the representation, obtained t-he aperture average of class A-shaped pores and class B-shaped pores e was between930nm-1540nm, the aperture average class C-shaped pores was between540nm-910nm.the shape of class A-shaped pores was irregular, while the shape of class B-shaped pores and class C-shaped pores was regular. The results of potentiodynamic polarization curves and electrochemical impedance spectroscopy analysis showed that three different types of pores had different effects on the corrosion performance:the anodic oxide film with class A-shaped pores with the corrosion potential around-0.80V. the impedance value of porous layer were respectively300KQ,250KΩ. and a826KΩ:the anodic oxide film with class B-shaped pores with the corrosion potential around-0.49V to-0.66V, the impedance value of the porous layer were respectively19000KΩ,12690KΩ,14400KΩ,43170KQ and29150KfΩ; the anodic oxide film with class A-shaped pores with the corrosion potential about-0.7V. the impedance value of the porous layer were respectively2096KΩ.2287KQ and10610KΩ. The different electrochemical parameters of the different oxide film showed that regular pores was more conducive to sealing than the irregular one, opening pores was more conducive to sealing than a sharp pores, the oxide film with pores which was sleek and broad opening has the best corrosion resistance after sealing. |
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