過錳酸根對AZ31鎂合金磷酸／錳酸鹽化成皮膜結構與性質之影響

Effects of Permanganate on the Structure and Properties of Phosphate/Permanganate Conversion Coatings on AZ31 Magnesium Alloy

李偉任(W. J. Li) ； 李威志(W. C. Li) ； 褚喻仁(Y. R. Chu) ； 林招松(C. S. Lin)

《防蝕工程》 21卷2期 (2007/06) Pp. 109-115

摘要

鎂合金爲目前全球輕量化與節約能源的關鍵材料，為了改善鎂合金極易腐蝕的特性，鎂合金工件上常需進行表面改質。本研究探討化成處理中過錳酸根濃度對AZ31鎂合金磷酸／錳酸鹽化成皮膜結構、抗蝕性與附著性的影響。交流阻抗結果顯示在60℃化成液中，增加過錳酸根濃度可提升皮膜阻抗以及抗蝕能力，在鹽霧試驗中發現化成液中過錳酸鉀含量為40g/L時皮膜抗蝕能力最佳。在SEM表面觀察發現提升化成液中過錳酸根濃度，化成皮膜裂紋寬度減小且緻密化，另由百格試驗結果顯示錳酸根濃度大於40g/L時，脫落面積低於15%，附著性提升。製作橫截面TEM試片觀察得知皮膜組織為多層結構，利用EDX偵測出皮膜錳含量由內向外增加。當溶液中過錳酸鉀含量增加會導致皮膜錳含量上升。並使用XPS解析出表層錳為四價錳的訊號。

關鍵字

磷酸／錳酸鹽化成處理 ； 交流阻抗 ； 鹽霧試驗 ； 百格試驗

並列摘要

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 40g/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 40g/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.

並列關鍵字

Phosphoric/permanganate conversion coating ； AC impedance ； Salt spray test ； Adhesion