氟化钾对AZ91D镁合金微弧氧化膜的生长及微观结构的影响

通过在NaOH和Na_2SiO_3组成的基础电解液中,分别不加及加入KF,对AZ91D镁合金进行微弧氧化处理,研究了KF的有无对镁合金微弧氧化膜的生长、微观结构及耐蚀性能的影响。结果表明:与不加KF相比,加入KF后,试样的起弧电压明显降低,击穿变得剧烈,试样表面火花较大,膜层的生长速率明显提高,膜层厚度显著增大,表面孔隙率稍有增大,但表面微孔数量减少。KF的加入有利于MgF_2、MgAl_2O_4的生成,与同样来自电解液的Si、O两元素相比,F~-更易被基体中的Mg所吸附,也容易通过已成膜层迁移到膜层的内部。电解液中含有KF时,膜层厚度显著增大,MgAl_2O_4物相含量增加,并生成新物相MgF_2,这些都有利于膜层耐蚀性的提高。

Effect of potassium fluoride on growth and microstructure of MAO coatings on AZ91D magnesium alloys

AZ91D magnesium alloys were processed in the base electrolyte composed with sodium hydroxide and sodium silicate, not containing or containing potassium fluoride respectively, by micro arc oxidation (MAO). Influence of potassium fluoride on growth, microstructure and corrosion resistant of the coatings was investigated. The results show that after potassium fluoride was added to the base electrolyte, the breakdown voltage to the specimen decreased but the breakdown process was more vigorous to lead to formation of larger sparks on the specimen surface during micro arc oxidation. As a result, the grow rate of the coating significantly increased and the obtained coating had a remarkable improvement in terms of coating thickness. Meanwhile, the surface porosity of the coating somewhat increased but the amount of the micro-pores on the coating surface decreased. The addition of potassium fluoride into the electrolyte is helpful for the formation of MgF₂and MgAl₂O₄ phases of the coating. Compared with silicate and oxygen elements from the electrolyte, F_- ion is more likely to be adsorbed by magnesium in the substrate and also easily overcomes the obstacle of the generated coating to migrate into the inner of the coating. The corrosion resistance of the coating treated in the electrolyte with potassium fluoride is increased under the influence of significant increasing in coating thickness mainly and the existence of favorable phases such as MgF₂ newly born and more MgAl₂O₄.,