Improvement of Hardness and Corrosion Resistance of Aluminum Alloy by Ceramic Coating Using Sol-Gel Method

Hiroyasu TSUGE*, Yasuo NISHI, Michiyuki KUME and Satomi ONO

Nagoya Municipal Industrial Research Institute; 3-4-41, Rokuban, Atsuta-ku, Nagoya-shi 456-0058 Japan

Silica, zirconia and silica-zirconia double coating films were prepared on aluminum alloy (ADC12) using the corresponding metal alkoxides and poly (vinyl butyral) as starting materials, and the hardness and corrosion resistance of these films were examined. First, in order to prepare silica films having appropriate thickness, the composition of the precursor solution was optimized. As a result, it was found out that 0.5 mol dm−3 tetraethoxysilane in ethanol solution, which was prepared by mixing of tetraethoxysilane, acetic acid and water in the molar ratio of 1 : 3 : 2 including 1 wt% poly (vinyl butyral), and concentrating by heating, was the most suitable for coating. Using this precursor solution, silica, zirconia and silica-zirconia double coating films were prepared. Vickers hardness of the coated alloy was measured, finding that the hardness of silica-coated ADC12 was about three times larger than that of bare ADC12, and the hardness of the zirconia or silica-zirconia coated ADC12 was about ten times larger than that of bare one. Furthermore, the corrosion resistance test using an aqueous solution of copper sulfate indicated that silica-zirconia coating inhibited the corrosion of the ADC12 effectively.

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