| Summary: | 博士 === 國立高雄應用科技大學 === 機械工程系 === 105 === Aluminum alloy has better mechanical properties than pure aluminum, and has become widely used in daily life and in industry. Porous anodized aluminum oxide (AAO) prepared in the standard process of anodization is naturally pigmented, and sometimes referred to as naturally pigmented AAO. This thesis examines the characteristics of an oxide film grown in a single anodizing process of aluminum alloy 6061-T6. The optimized anti-reflective film obtained by changing the process parameters has already begun to receive considerable recognition and attention.
The research directions can be categorized as: a study on anodizing aluminum alloy 6061-T6 in sulfuric acid in a single hard anodizing process in order to prepare a selective absorption structure with a high aspect ratio, and an investigation into the effects of electrolytic polishing during the anodization pretreatment process on the surface appearance and optical properties. Anodic oxide films are primarily amorphous, and the characteristics of the films are most significantly influenced by the current and the temperature of the electrolytes. It was found that the variation in roughness, contact angle, and oxygen content of the substrate itself were proportional to its roughness. In regards to the process temperature, it was found that lower rated voltages resulted in more complete surface structures, and the pore size, film thickness, and processing temperature were all proportionally related. Furthermore, higher processing voltages caused lower temperatures, which damaged the surface structure and resulted in irregular formations. Observations using rated voltage at a temperature of 0℃ revealed an increase to the proportionality of pore size, thickness, and voltage. Additionally, the larger the current, the faster the reaction rate, increasing the thermal energy and resulting in a higher the corrosion rate. This further resulted in an increase to the pores and porosity, as well as a looser film, which led to a decrease in the hardness and withstand voltage. During the anodizing process, expanding of the oxide film created excess stress and produced cracks.
Spectral measurements of the substrate revealed an absorption peak in a band of 850 nm, and its reflectivity was affected by the Fresnel reflection causing the reflection to increase with the increase of the angle. In the cases of complete structures, pore size and film thickness were inversely proportional to the average reflectance; incomplete structure tended to result in scattered color and irregularities in the reflectance. No linear changes were observed in the solar thermal efficiency and average reflectance when changes were made to the rated voltage while maintaining a fixed temperature. The porous anodic oxide film with a high aspect ratio obtained using a temperature of 0℃ and rated voltage of 50V had relatively low average reflectance and relatively high thermal efficiency.
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