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

通过改变硅酸盐体系电解液中KF和Na_(2)SiO_(3)的浓度,定量分析氟化钾与硅酸钠浓度配比(简称氟硅比)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Na_(2)SiO_(3)在微弧氧化成膜中必不可少。当电解液中含有KF时(氟硅比大于0),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,且由于KF在电解液中的存在,会生成新物相MgF_(2),促进物相Mg_(2)SiO_(4)的形成,这些物相有利于提高膜层的耐蚀性。此外,KF与Na_(2)SiO_(3)二者在成膜反应中的竞争与协同作用因氟硅比的变化而变化,致使膜层的微观结构与物相含量随之改变,从而影响膜层的耐蚀性。本研究中,当氟硅比为0.5(KF:Na_(2)SiO_(3)=7.5:15)时,由于KF与Na_(2)SiO_(3)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,是最佳的氟硅比。

AM60 B 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 Na_(2)SiO3 in electrolytes.The results show that the main salt Na_(2)SiO3 is essential in the film-forming reaction.When the coatings are treated in the electrolyte with potassium fluoride(fluoride-silicate ratio is greater than zero),the film-forming reaction is intensified with the increasing of fluoride-silicate ratio,which causes the coatings owning more surface porosity,more number of large pore(>3μm),and larger thickness.And newly formed MgF2 and more Mg_(2)SiO_(4)in the coatings because of the existence of KF in the electrolyte will contribute to the improvement of the coatings’anti-corrosion ability.In addition,the competitive and synergistic effect of KF and Na_(2)SiO3 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 the present paper,the best fluoride-silicate ratio is 0.5(KF:Na_(2)SiO3=7.5:15),since the resulting coating has shown a larger thickness,better density and fewer defects due to the good synergism between KF and Na_(2)SiO3.That is to say,both large thickness and excellent corrosion resistance of the coating has been obtained at this point.