| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 104 === Magnesium and its alloy have been used widely for the living facilities and military defense owing to their excellent physical and mechanical properties, such as low density, high strength, good cast-ability and weld-ability, excellent electrical and thermal conductivity, high dimensional stability, good electromagnetic shielding and high recyclability. However, the poor corrosion resistance of magnesium alloys have limited their engineering applications, especially in acidic environment and salt-water conditions.
Two processes were used to improve the corrosion resistance of the magnesium alloys, including sputtering and anodized. Since the aluminum film is more stable than magnesium substrate, the aluminum film can be oxidized to aluminum oxide film, to further improve the corrosion resistance. In this study, the sputtering + anodized were carried out on an AZ91D Mg alloy, and the effects on the corrosion resistance were evaluated.
The cross-sectional configuration of film was analyzed by Dual Beam Field Emission Focused Ion Beam (DB-FIB), indicated thickness of anodized oxide films increased with the oxide time. The film surface is characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) which indicated that the anodized oxide layer was amorphous structure and composed by Al2O3.
The results of potentiodynamic polarization show that the sputtering Al film and the anodized oxide layer on the AZ91D alloys performed more positive corrosion potential and lower corrosion current density than the AZ91D substrate, by adopting an anodizing treatment 15 minutes specimen have higher corrosion potential value of -1.359 V and lower corrosion current density value of 0.262 μA/cm2. Similar, according to EIS results, the charge transfer resistance of the anodized specimens were larger than the AZ91D substrate. These results proved that the sputtering Al film with anodizing treatment coated on the AZ91D alloys significantly improved the corrosion resistance property of the AZ91D alloys.
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