| 英文摘要 |
Magnesium alloys have low density and high strength/weight ratio, making them potential structural materials in the applications where energy consumption and light weight are the major concern. Because magnesium is relatively reactive, surface modification treatments are extensively used to improve the corrosion resistance of magnesium alloys. This study investigated the effects of solution permanganate concentration on the formation, corrosion resistance, and adhesion of phosphate/permanganate conversion coating on AZ31 magnesium alloys. Increasing permanganate anions in the electrolyte at 60 ℃ resulted in the conversion coating with improved polarization resistance, as characterized by AC impedance. Nevertheless, the salt spray test revealed that the coating formed in the solution containing intermediate amounts of potassium permanganate, namely 40 g/L, had the best corrosion resistance. More compact coatings with less and smaller cracks were made in the solution containing more permanganate anions. Moreover, the coating formed in the solution to which more than 40 g/L potassium permanganate were added underwent less than 15% (in area fraction) peel off after adhesion test. Cross-sectional TEM revealed that the coating consisted of three layers in which more manganese were detected in the outer layer. Furthermore, more manganese species were incorporated in the outmost layer of the coating formed in the solution containing more permanganate anions. These manganese species were likely the tetra-valent manganese as characterized by XPS. |
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