Preparation And Corrosion Resistence Of MAO/Ta₂O₅ Composite Coating On Magnesium Alloy

Magnesium alloy has the advantages of low density,high specific strength and high specific rigidity,and has broad application in automobile manufacturing,aerospace and biomedicine.However,the active nature of magnesium and its alloys makes it extremely susceptible to corrosion,which limits its application to a certain extent.Micro-arc oxidation technology can be applied to the modification of the surface of magnesium alloys.By growing ceramic films in situ on the surface to form a new structure and composition,it can improve its corrosion resistance.However,due to the limitations of the micro-arc oxidation process conditions,the prepared ceramic membrane has micrometer-scale holes and a small number of micro-cracks,which limits its protection of the magnesium alloy substrate.Ta₂O₅ has good corrosion resistance and chemical stability.The MAO/Ta₂O₅ composite film was prepared on the AZ31B magnesium alloy substrate by two experimental methods.The micro-arc oxide film can be modified to further improve its corrosion resistance.The thesis use magnetron sputtering-micro-arc oxidation composite surface treatment technology.First,a layer of Ta film is coated on the substrate,followed by micro-arc oxidation treatment to generate a MAO/Ta₂O₅ composite film.The experiment investigated the influence of sputtering time,sputtering power,oxidation time and current density on the surface morphology,electrochemical performance,phase composition and salt spray corrosion resistance of the composite film.The results show that the corrosion resistance of the prepared composite film is optimal when the sputtering power is 40W,the sputtering time is 90 min,the oxidation time is 20 min,and the current density is 15 m A/cm².At this time,the corrosion current density was 2.4×10^-9 A/cm²,and the corrosion potential was-1.28 V.After 14 days of salt spray corrosion test,the corrosion degree was the lightest.XRD and XPS indicate that the composite film is mainly composed of Mg O,Ta₂O₅ and Mg₂Si O₄,but some Ta has not completely reacted into Ta₂O₅.In this paper,MAO/Ta₂O₅ composite membranes are prepared in one step by adding Ta₂O₅ nanoparticles directly in the micro-arc oxidation electrolyte.The influence of the concentration of Ta₂O₅ nanoparticles on the surface morphology,electrochemical performance,phase composition and salt spray corrosion resistance of the composite film was studied experimentally.The results show that the addition of Ta₂O₅ can change the porosity and uniformity of the film to varying degrees.When adding 4 g/L Ta₂O₅nanoparticles,the pore size of the composite film is the smallest and uniformly distributed,the corrosion current density drops to 2.36×10^-9 A/cm²,the corrosion potential is moving to-1.30 V,and after 14 days of salt spray No obvious corrosion spots after the corrosion test.EDS,XRD and XPS test results show that the composite film is mainly composed of Mg O,Ta₂O₅ and Mg₂Si O₄,and Ta₂O₅ nanoparticles are inertly embedded in the membrane layer.By comparing and analyzing the MAO/Ta₂O₅ composite films prepared by the two methods,the chemical composition of the composite films prepared by the two methods is similar,mainly Mg O,Ta₂O₅ and Mg₂Si O₄,but the composite prepared by the magnetron sputtering-micro-arc oxidation method Some unreacted Ta exists in the film.The corrosion current density of the composite films prepared under their respective optimal parameters is particularly close,and the corrosion resistance of the film layers is similar,but the preparation process of the one-step micro-arc oxidation method is simple,the cost is low,and the advantages are more obvious in this study.