化成電壓對鋁陽極氧化膜電化學腐蝕阻抗行為的影響

Effect of Forming Voltages on the Electrochemical Corrosion Resistance Behavior of the Microarc Oxidation Films of Aluminum Alloy

鋁陽極氧化膜可用於增進鋁材的抗腐蝕性，工業上鋁陽極處理過去大多在酸性溶液中進行；本研究嘗試在鹼性氫氧化鈉溶液並加入水玻璃，改變各種化成電壓（50 V～350V）進行鋁陽極處理後，將所有試片置於0.05M H2SO4水溶液中，利用電化學方法探討各種不同化成電壓所生成的陽極氧化膜之電化學腐蝕阻抗行為。使用掃描式電子顯微鏡（SEM）和化學分析電子儀（ESCA）對不同化成電壓形成之陽極氧化膜進行表面型態及組成的分析。電化學腐蝕阻抗量測試驗，包括直流（DC）線性極化、定電位動態極化，以及交流（AC）阻抗頻譜（EIS）。結果顯示鋁材經陽極氧化處理後，均有較貴性（noble）的電位、較高的極化阻抗（Rp）、以及較低的腐蝕電流密度（icorr），定電位動態極化行為也顯示較低的陽極極化電流密度；而且所有陽極氧化膜之直流腐蝕阻抗性均隨著化成電壓之升高而增加。在交流阻抗頻譜試驗方面，鋁陽極氧化膜除了顯現電化學極化阻抗（Rp）均比鋁基材高而且也隨化成電壓升高而增加外，在化成電壓250V以上所生成之陽極氧化膜，由於電漿電弧的作用，其極化阻抗（Rp）可增大為鋁基材的十倍（由2000Ω增至20000Ω），而形成了更緻密的腐蝕保護陽極氧化膜。

Anodic aluminum film can be applied to increase the corrosion resistance properties of Al-alloy. In industry, aluminum acid anodizing was usually processed in acidic solution in the past. This study tries to use the solution of alkaline NaOH and add the Na2SiO3 modification to it. After changing various forming voltages (50 V~350 V) and processing the materials by microarc anodizing, all of them are put in 0.05M H2SO4 solution, using electrochemical measurement to probe into the electrochemical corrosion resistance behavior of anodic oxidation film caused by different forming voltages. The result shows that during the process of anodizing, when the forming voltage rises to 250 V, a clear and obvious plasma arc will appear. When aluminum is after processed by anodizing, it has noble potential, higher Rp and lower icorr. In the test of Electrochemical Impedance Spectroscopy(EIS), in addition to Rp increasing with the rise of forming voltage, the Rp of the anodic aluminum film forming when the forming voltage is above 250 V can increase to tenfold compared with Al-alloy(e.g. from 2000Ω to 20000Ω ) due to the action of plasma arc. Thus it forms more delicate correction to protect the anodic oxidation film.