| Summary: | 碩士 === 國防大學理工學院 === 化學工程碩士班 === 105 === Magnesium is chemically active and Mg-Li alloys tend to suffer corrosion during services, signifying the necessity of surface modification. A micro-arc oxidation treatment was developed in this study for LZ91 magnesium alloys. Modified power modes (DC, unipolar pulses, and bipolar pulse) were systematically studied. The morphology and the coating thickness was observed and determined by using SEM. The corrosion behavior of the coated samples was evaluated by potentiodynamic polarization tests and salt spray test. The experimental SEM images were interpreted using the Image J to count the number and the size of the micro-pores. These results indicated that the bipolar pulses treatment on LZ91 alloys may provide the best corrosion protection. It can be easily noted that the coatings exhibited both the thick thickness and the much finer pores, and the resulting coating does not suffer corrosion exceed 48h of salt spray test.
As a result, increasing size of the micro-cracks or micro-pores on the coated surface, where corrosion proceeded in the film. And, the micro-pores size was 8 μm exhibits best corrosion resistance, suggesting its better passivation properties.
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