| Summary: | 碩士 === 中正理工學院 === 兵器系統工程研究所 === 87 === Metal matrix composites (MMCs) have been applied in many application fields, such as aerospace, national defense and civil industries for a long time. The superior mechanical properties are the major reasons for various applications, but the weaker corrosion resistance of them is a factor that should be studies. There are many kinds of corrosion types that take place between the matrix and the reinforcement particles, for example: galvanic corrosion, selective corrosion, crevice corrosion and so on. Anodizing technique is an effective surface treatment for improving the corrosion and wear resistance of MMCs, such as aluminum matrix composites.
The anodizing technique is an electrochemical method to convert aluminum into aluminum oxide (Al2O3 ) by applying an external current to the electrolyte. Aluminum matrix composites, Al2O3/6061-Al and SiC / A356-Al, with various reinforcement concentrations have been compared with pure aluminum. Sulfuric acid has found to be a preferred anodizing electrolyte for the composites, as it allowed a relatively thick anode film to be formed on the surface. The properties of anode film have been changed by five parameters in this study: electrolyte concentration, electrolyte temperature, current density, growth time, and sealing condition. These samples have been passed through different kinds of tests, in order to find more suitable parameters. These include microhardness test, film thickness measurement, microstructure examination, surface roughness scanning, corrosion test and wear resistance test.
The anodic film thickness of specimen increases with increasing reinforcement concentration, but corrosion and wear resistance decrease. The larger holes have located above the reinforcement particles of the composite surface. The thicker film is employed for wear resistant applications, and therefore , the higher current density (5A/dm2) has been used to make it. Because the surface is too rough, it was not necessary for hot-water sealing. Coating for corrosion resistance is typically thin, so the coating time has to increase to 50 minutes and the current density decreases to 1A/dm2. It is essential to seal the cell as to increase the ability of corrosion resistance. When other parameters should be kept in the standard state or at lower temperature, the increase of electrolyte concentration and temperature will decrease corrosion and wear resistance. Finally, the influences of the parameters of anode film quality in MMCs in turn are current density, growth time, electrolyte temperature, and electrolyte concentration.
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