| Magnesium alloys are widely used in aviation,aerospace and machinery and other fields because they excellent performance.However,magnesium alloys have high electrochemical activity and poor corrosion resistance,which seriously limit their application in engineering.Therefore,it is necessary to adopt the corresponding surface treatment technology to improve the corrosion resistance of magnesium alloys.Micro-arc oxidation is one of the surface treatment technologies for magnesium alloys in recent years.Micro-arc oxidation is a surface modification technique for in-situ growth of ceramic coatings on magnesium alloys.The paper use AZ31B magnesium alloys as substrate,the effects of sodium silicate concentration,sodium hydroxide concentration,current density,oxidation time and sodium pyrophosphate concentration on the appearance,thickness and hardness of AZ31B magnesium alloy micro-arc oxidation coatings were studied by a large number of preliminary exploration experiments and orthogonal experiments,and the optimum process parameters of AZ31B magnesium alloy were determined.On the basis of the optimization of process parameters,through adding Sb2O3 particle into the micro-arc oxidation electrolyte,it study the effect of different concentration of Sb2O3 on AZ31B magnesium alloy micro-arc oxidation coating growth process,the structure of the morphology,coatings composition and properties by SEM,EDS,XRD and XPS analysis method,and discusses the Sb2O3 micro-arc oxidation doping mechanism.Orthogonal experiment research shows that when temperature is low than 30?,duty ratio of 20%,and frequency of 100 Hz,optimization of process parameters is:Na2SiO3 10.5 g/L,NaOH 3 g/L,oxidation time of 60 min,current density of 5 A/dm2,Na4P2O7 2 g/L.Based on the optimal process,Sb2O3 particles of Og/L,1g/L,2g/L,3g/L and 4g/L were respectively added to study the influence of different Sb2O3 particle concentrations on the properties of AZ31B magnesium alloy micro-arc oxidation coatings.The results showed that the addition of Sb2O3 could significantly change the properties of the coating and improved the corrosion resistance of the magnesium alloy.Sb2O3 migrated to the surface of the anode sample under the action of electric field and mechanical stirring,and the increase of coating resistance increased the oxidation voltage of the coating,thus the addition of Sb2O3 could promote the growth of the coating.It is found that adding appropriate concentration of Sb2O3 in the electrolyte can significantly improve the properties of the coating.Because Sb2O3 was mixed with melt or embedded in the discharge channel,it could change the morphology structure of the coating,and further improved the performances of the coating.However,excessive Sb2O3 would lead to partial discharge of the sample during micro-arc oxidation,which made the coating rough and porous,and it resulted in the degradation of coating performances.The structure of coatings were porous,and mainly composed of MgO,Sb2O3 and Si02.The oxidation voltage provided the energy of the coating growth during the micro-arc oxidation process.The change of the oxidation voltage affected the coating formation process.With the increase of Sb2O3 concentration,the oxidation voltage first increased and then decreased,so the thickness of the coating increased first and then decreased.At the same time,the micro-pore size of the coating decreased first and then rose with the change of voltage,which resulted in the density of coating increase firstly and then decrease.The hard phase and the dense coating increased the hardness,and the coating thickness and hardness together caused a change of coating adhesion.Due to the thicker coating and dense structure,it was difficult for Cl-to pass through coating,so the corrosion resistance of coating increased.Therefore,with the increase of Sb2O3 concentration,the thickness,hardness,adhesion,and corrosion resistance of coatings showed a trend of increase and then decrease. |
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