Research On Hydrothermal Preparation And Corrosion Properties Of Zirconia Base Coatings On Magnesium Alloys

As the lightest metal structural material,magnesium alloy has the advantages of low density,high specific strength and specific stiffness,good reusability,strong vibration reduction,good machinability,etc.It is widely used in automobile,electronics,aviation,military industry and other fields,but because of low electrode potential and easy corrosion of magnesium,it has become a bottleneck problem restricting the application of magnesium alloy.Therefore,corrosion and protection of magnesium alloys has become a research hotspot in this field.Due to the complex friction environment encountered in the application of magnesium alloy in the automotive field,if the protective layer of magnesium alloy has poor wear resistance and easy to wear,when the protective layer is worn,it will lose its protective effect on magnesium alloy components.Therefore,the protective coating of magnesium alloy should not only be corrosion resistant,but also have certain wear resistance to prolong the service life of the protective coating.Zirconia ceramic material has attracted much attention because of its excellent corrosion resistance,good chemical stability,high hardness,high wear resistance and excellent thermoelectric properties.In recent years,it has been used as an effective protective coating for metal substrates.In this paper,zirconia(ZrO₂) based coatings were prepared on the surface of magnesium alloy by hydrothermal method,including in-situ ZrO₂coatings,phytic acid/ZrO₂coatings and polydopamine/ZrO₂coatings.The morphology,composition,hardness,adhesion and corrosion resistance of the prepared coatings were systematically investigated.The main work and conclusions are as follows:(1)ZrO₂film was successfully prepared on the surface of magnesium alloy by hydrothermal method.The effects of etching pretreatment and hydrothermal time on the morphology,thickness,adhesion and corrosion resistance of the prepared films were investigated.The results show that the ZrO₂film prepared by hydrothermal reaction for 12h is the flattest and densest,and its hardness and corrosion resistance are also the best.Etching pretreatment can effectively improve the adhesion between coating and substrate.(2)Phytic acid/ZrO₂ film was prepared on the surface of magnesium alloy based on the above hydrothermal method.The effects of hydrothermal time on the morphology,thickness,adhesion and corrosion resistance of the prepared film were investigated.The results show that the film prepared by hydrothermal reaction for 12h is compact and has no crack,and the film is closely bonded with the substrate,and has no crack.The adhesion and corrosion resistance are also the best.Compared with the exposed AZ61,the hardness is increased by 19.2HB,and the corrosion resistance is increased by an order of magnitude.Compared with the ZrO₂film prepared in situ,the adhesion reaches grade 4B,which is an increase of one grade.(3)Inspired by the clam adhesion phenomenon in nature,polydopamine/ZrO₂film was prepared on the surface of magnesium alloy in order to further improve the adhesion and reduce the corrosion of magnesium alloy before the coating of ZrO₂film.Compared with ZrO₂film,the thickness of polydopamine/ZrO₂composite film was significantly increased,indicating that polydopamine could induce the deposition of ZrO₂,and the thickness of polydopamine/ZrO₂composite film was 79.9?m.The polydopamine/ZrO₂film did not fall off after the adhesion test,and the adhesion reached grade 5B.The corrosion resistance of polydopamine/ZrO₂film is better than that of ZrO₂and polydopamine film.