| Summary: | 碩士 === 大葉大學 === 電機工程學系 === 103 === A green and environmental friendly trivalent chromate conversion treatment on electrodeposited Zn-Ni alloy coating was studied in the paper. Zn-Ni alloy coating was first electroplated on steel substrate by using basic solution bath. Then, the surface of the Zn-Ni coating was subjected to trivalent chromate passivation in three different conversion durations: 10 s, 30 s and 60 s, respectively. The 3-µm Zn-Ni coating consisted of 15-17 wt% in Ni and showed dominant (330) columnar crystallite under TEM examination. The preferred orientation in (330), along with minor diffraction peaks in (600), (444), (552), (741) and (660), was further confirmed with X-ray diffraction measurement. XPS evaluation revealed the passivation film composed of Cr2O3, ZnO and NiO. With increasing conversion duration, both Zn and Ni contents decreased, but the oxygen content increased. Furthermore, based on the content ratio between Zn and Ni, the passivation film became relatively rich in Ni. Through TEM microscopy, the thickness of the passivation film was between 90-340 nm and became more uniform with increasing conversion duration. There existed tiny porous structure in the trivalent chromate film which evolved into similar porous nature but larger in size and more in number as the conversion duration increased. The result of the polarization measurement showed that the passivation film with 30-s conversion treatment possessed the best corrosion resistance. It is found that the passivation film with more uniform thickness, less porous nature, and certain Ni/Zn content ratio was better in corrosion resistance.
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