重複浸泡對AZ31鎂合金硝酸鈰化成處理的影響

Effects of Repeated Immersions on the Formation of Cerium Nitrate Conversion Coatings on AZ31 Magnesium Alloys

鎂合金具有低比重、高比剛性、高制震能、電磁遮蔽效應、可回收等優點，已被廣泛應用在3C產業、娛樂產品與航太運輸上，但使用上必須考慮高溫潛變、抗蝕性等問題。本研究在AZ31鎂合金表面進行硝酸鈰化成處理，使用重覆浸泡方式成長化成皮膜，提升皮膜附著性及抗蝕性。實驗期間搭配開路電位（Open Circuit Potential, OCP）量測皮膜成長穩定之電位和時間，並以掃描式電子顯微鏡（SEM）觀察皮膜形貌，以穿透式電子顯微鏡（TEM）觀察化成皮膜結構和厚度。量測極化曲線及交流阻抗，評估皮膜抗蝕能力和皮膜阻抗，皮膜附著性參照ASTM D3359-97百格試驗方法。實驗結果顯示重複浸泡後，皮膜裂紋及缺陷減少，對於附著性和抗蝕性有顯著提升的效果。

Magnesium alloys have benefits of a low density, high specific strength and stiffness, excellent damping qualities, good EMI shielding and recyclability. For these reasons magnesium alloys are extensively used in 3C components, entertainment products and aerospace applications. Major concerns over using magnesium alloys are creep and corrosion. This study was aimed to investigate the effects of repeated immersions in cerium nitrate solutions on the formation, corrosion resistance and adhesion of the coating. The open circuit potential was measured for tracing the formation rate of the coating. The surface morphology was examined by SEM and the coating structure and thickness were characterized by cross-sectional TEM analysis. Moreover, the corrosion resistance and impedance of the coating were measured by polarization test and ac impedance spectroscopy. The adhesion test was conducted in accordance with ASTM D3359-97. The results showed that the process of repeated immersions increased the coating adhesion and corrosion resistance.