Preparation Of The Magnesium Alloy Micro-arc Oxidation Film Reinforced By Powder

Magnesium alloy has been widely applied in automobile production,electronic processing,aerospace and other fields because of its good electrical conductivity and mechanical processing properties.However,the lower potential of magnesium alloy and the more active chemical properties make its corrosion resistance less.In this paper,a micro-arc oxidation film of magnesium alloy was prepared by using silicate electrolyte.Its performance was characterized by droplet test,electrochemical workstation,metallographic microscope,scanning electron microscopy（SEM）and X-ray diffraction（XRD）.And various additives and powder additives were studied to determine the best magnesium alloy micro-arc oxidation film preparation process.The experiment studied the effects of sodium silicate,triethanolamine,sodium tetraborate and sodium hydroxide on the performance of micro-arc oxidation film in the preparation process of magnesium alloy base silicate micro-arc oxidation film.The orthogonal experiment and single factor experiment optimized the best technological parameters of magnesium alloy micro-arc oxidation film,which were sodium silicate50g/L,triethanolamine 20g/L,sodium tetraborate 22.5g/L,sodium hydroxide 20g/L,transformation temperature 25℃and transformation time 30min.The test results showed that the corrosion potential of micro-arc oxidation film moved forward 0.588V comparing with the magnesium alloy substrate.The corrosion current density was obviously reduced by two orders of magnitude.The corrosion resistance of the oxide coating was improved.The effects of five additives,including glycerin,EDTA,cerium nitrate,sodium benzoate and potassium hydrogen phthalate,on the performance were studied in the experiment.The results showed that the surface of the film with 3g/L sodium benzoate was flat,smooth,without obvious protrusions and dents.The size of the holes was equal.The dripping time was higher than the other four additives,which was more 33s than without any additive.It had the smallest corrosion current 2.916×10^-7A/cm²,the largest polarization resistance 94456?and the largest AC impedance arc radius.The micro-arc oxidation film with 3g/L sodium benzoate had the lowest weight loss after etching 72h,which improved micro-arc oxidation film surface morphology and corrosion resistance.Nano-scale Fe,Ti,Al₂O₃ and Y₂O₃ powder were added to the electrolyterespectively to prepare the composite micro-arc oxidation coating on the surface of the magnesium alloy.The effects of powder types and additives amount on the performance of the film were studied to determine the optimal electrolyte formulation and powder addition amount.The results showed that powder can make the film smoother,hole edge smooth,equal size,better coverage after adding Y₂O₃.A large number of Y₂O₃ powders entered into and adhered to the holes to make the pore of the film decrease obviously and more uniform.The film phase composition increased Y2O3phase,in which Y,O two elements significantly increased.The dripping time was higher than the other four additives after adding nano Y₂O₃ powder coating,which was almost more 31s than without any additive.It had the smallest corrosion current1.227×10^-7A/cm²and the largest polarization resistance 122687?.The micro-arc oxidation film with adding nano Y2O3 powder had the lowest weight loss after etching72h,which improved micro-arc oxidation film surface morphology and corrosion resistance.