AZ91镁合金表面微弧氧化与化学镀铜复合处理层的微观组织与性能

Microstructure and Property of Composite Coatings on AZ91 Mg-alloy Prepared by Micro-arc Oxidation and Electroless Cu-layer

采用微弧氧化技术在AZ91镁合金表面制备Mg O陶瓷膜层,然后在该膜层通过化学镀铜技术制备金属铜层。利用SEM,XRD,EDS,电化学实验及四探针测试等手段研究了复合膜层的显微结构、相组成、耐蚀性和导电性。结果表明:微弧氧化处理获得以Mg O为主相的陶瓷层可有效提高镁合金的耐蚀性,平均厚度为2.5μm的化学镀铜层连续均匀地覆盖在微弧氧化陶瓷层表面,渗入并填充微弧氧化陶瓷层内部呈网状分布的孔隙,形成交错咬合状态;复合膜层表面的导电性良好,与基体镁合金相比,复合膜层的腐蚀电位提高了0.2 V,腐蚀电流密度下降了一个数量级。但由于化学镀铜层与基体镁合金之间产生的电偶腐蚀,导致复合膜层的耐蚀性较陶瓷层有所下降。

MgO ceramic coating was prepared firstly on AZ91 Mg-alloy by micro-arc oxidation（MAO）,and on which then a Cu-layer was deposited by electroless copper plating. The microstructure, composition, corrosion resistance and electrical conductivity of the composite coating were characterized by means of SEM, XRD, EDS, electrochemical techniques and four-point probe test. The results indicate that the corrosion resistance of Mg-alloy can be effectively improved due to the existence of the ceramic MAO coating, and the 2.5 μm-thick Cu-layer is evenly covered on the surface of MAO coating, while the deposited Cu penetrates and fills the reticular-like pores on the MAO coating and thus to realize a mechanical interlock between the Cu-layer and the MAO coating. The composite coating exhibits well electrical conductivity. Meanwhile, the free corrosion potential of the composite coating increases by 0.2 V, and the corrosion current density is one order of magnitude lower in comparison with the bare Mg-alloy. However, the corrosion resistance of the composite coating is inferior to that of the MAO coating because of the galvanic corrosion between the Cu-layer and the matrix Mg-alloy.