AZ31B镁合金表面微弧电泳复合膜层微观结构及耐蚀性表征

Microstructure and Corrosion Properties of Micro-Arc Oxidation Composite Electrophoretic Coating on AZ31B Magnesium Alloy

摘要:

采用微弧氧化技术在AZ31B镁合金表面制备陶瓷层，利用其表面多孔结构借助电泳技术沉积有机膜层，对比研究陶瓷层和复合膜层表面粗糙度、表面及截面形貌、电化学性能及划伤腐蚀特性。结果表明：陶瓷层表面放电微孔被电泳层完全填充并形成均匀膜层，复合膜层表面粗糙度明显降低；微弧电泳复合膜层腐蚀电流密度与陶瓷层和基体相比分别降低2个和4个数量级，极化电阻分别增大2个和4个数量级，腐蚀倾向降低；微弧电泳复合膜层电化学阻值与陶瓷层相比增加4个数量级，同时电容值降低4个数量级，耐蚀性显著提高；由于陶瓷层与电泳层的机械嵌合作用，复合膜层划伤腐蚀过程表现为基体腐蚀及陶瓷层与基体界面的破坏，复合膜层界面处结合完好。

Abstract:

Porous ceramic layers were prepared on AZ31B magnesium alloy by Micro-arc Oxidation (MAO), and then electrophoretic coat (E-coat) was deposited on MAO coated Mg alloy. The surface roughness, surface and cross section morphologies, electrochemical properties and scribed corrosion properties of the MAO layer and MAO composite electrophoretic (MAOE) coating were studied. The results indicate that the discharge channels on surface of MAO layer are completely covered by E-coat and the surface of MAOE coating is very smooth; as a result, the surface roughness decreases obviously. The corrosion current density of MAOE coating is two and four orders of magnitudes lower than that of MAO layer and bare Mg alloy, respectively, and the polarization resistance is two and four orders of magnitudes higher, respectively, suggesting that the corrosion trend decreases. The EIS resistance of MAOE coating is four orders higher than that of MAO layer while the EIS capacitance is four orders lower, and thus the corrosion resistance is improved uncommonly. Due to the mechanical interlock between the MAO layer and E-coat, the substrate is corroded seriously during scribed corrosion test, and the coating delaminating at the interface of MAO layer and substrate also occur. However the interface of MAOE composite coating is still compact.