氟硅比对AM60B镁合金微弧氧化膜微观结构及耐蚀性的影响

Effect of fluoride-silicate ratio on microstructures and corrosion resistance of micro-arc oxidation coatings on AM60B magnesium alloys

摘要:

通过改变硅酸盐体系电解液中KF和Na2SiO3的浓度，定量分析氟化钾与硅酸钠浓度配比（简称氟硅比）的不同对AM60B镁合金微弧氧化膜层微观结构及耐蚀性的影响。结果表明：主盐Na2SiO3在微弧氧化成膜中必不可少。当氟硅比大于0时，随着氟硅比的增大，成膜反应加剧，膜层表面的孔隙率和表面大孔（>3μm）数目增加，膜厚增加。电解液中F-的存在，生成新物相MgF2，促进物相Mg2SiO4的形成，这些有利于提高膜层的耐蚀性。此外，电解液中F-与SiO32-的竞争与协同作用会随氟硅比的变化而变化，因而改变膜层的微观结构与物相含量，影响膜层的耐蚀性。本文研究中，当氟硅比为0.5（KF：Na2SiO3=7.5：15）时，由于F-与SiO32-之间良好的协同作用，形成的膜层厚度较大，致密性较好，缺陷较少，此时膜层兼备厚度大与耐蚀性优的特性，是最佳的氟硅配比。

Abstract:

AM60B magnesium alloys were processed in sodium silicate based electrolytes by micro-arc oxidation (MAO), and the influence of the concentration ratio of potassium fluoride to sodium silicate (in short as fluoride-silicate ratio) on the microstructure and corrosion resistance of the coatings was quantitatively analyzed with changing the concentrations of KF and Na2SiO3 in the electrolyte. The results show that the main salt Na2SiO3 is essential in the film-forming reaction. When fluoride-silicate ratio was greater than zero, the film-forming reaction was intensified with the increasing of fluoride-silicate ratio, which caused the coatings owning more surface porosity, more number of large pore (> 3μm ), and larger thickness. And newly formed MgF2 and more Mg2SiO4 in the coatings because of the existence of the F- in the electrolyte will contribute to the improvement of the coatings’ anti-corrosion ability. In addition, the competitive and synergistic effect of F- and SiO32- in the electrolyte will vary with the changing of fluoride-silicate ratio, thus affecting the microstructure, phase content, and even the corrosion resistance of the coatings. In this paper, the best fluoride-silicate ratio was 0.5(KF: Na2SiO3 = 7.5:15), since the resulting coating has shown a larger thickness, better density and fewer defects due to the good synergism between F- and SiO32-. That is to say, both large thickness and excellent corrosion resistance of the coating has been obtained at this point.