磷酸盐-氢氧化钾溶液中镁合金微弧氧化膜层结构和性能研究

Study on structure and properties of microarc oxidation coating on magnesium alloy in phosphate-potassium hydroxide solution

在磷酸盐-氢氧化钾电解液中,利用微弧氧化技术在AM60B镁合金表面获得了氧化膜层。截面光学显微形貌与扫描电镜照片显示,该氧化膜层为一连续的整体,氧化膜与基体存在清晰的界面,界面附近无孔洞、裂纹等缺陷,而在氧化膜表面则分布着大量的微孔,并有微裂纹存在;EDS成分分析表明,膜层主要由Mg、A l元素(来自于基体)和P、O元素(来自于电解液)组成;X-射线衍射实验证明了微弧氧化处理在镁合金表面形成了一层以MgO为主要组成的氧化膜,但未检测到P的存在,由此说明P以非晶态的形成存在于膜层中。膜层截面硬度分布曲线和耐蚀性实验表明,膜层硬度随着膜层与界面距离的增加起初增大,在距离界面10μm处达到最大值为580HV,之后逐渐降低;基体与微弧氧化膜层在w(NaC l)=3.5%NaC l溶液中的极化腐蚀电流密度分别为198 A/cm2和3.54 A/cm2,说明微弧氧化膜的生成使镁合金的耐蚀性能明显增强。

The oxidation coating on magnesium alloy surface was obtained from electrolyte of phosphate-potassium hydroxide with microarc oxidation technics. Photos of crosssection optical microscope morphology and SEM show that the oxidation coating is continuous. The clear interface exists between oxidation coating and substrate. There aren＇t disfigurements of hole and crack existing about interface. Many microholes distribute on the surface of oxidation coating, and there are cracks on it. The EDS components analysis show that the coating consists of Mg, Al （gained from substrate） and P, O （gained from electrolyte）. X-ray diffraction experiment proves that the oxidation coating is mostly composed of MgO but without P. It indicates that P forms a non-crystal in the coating. The cross-section hardness distribution curve of coating and corrosion resistant test show that with increasing distance between coating and interface, the coating hardness increases firstly and reaches the maximum value of 580 HV at the distance of 10μm from interface, and then decreases. Polariration corrosion current density of substrate and microarc coating are 198 A/cm^2 and 3.54 A/cm^2 respectively in the solution of w （NaCl） = 3.5% NaCl. It shows that the corrosion resistance of magnesium alloy is increased due to the formation of oxidation coating.