Micro Arc Oxidation On AZ91D Magnesium Alloy And Research Of After-treatment

In this study,an eco-friendly alkaline electrolyte was used to treat the AZ91D magnesium alloys to form a ceramic membrane with good properties towards the adverse corrosion resistance of magnesium alloys.This alkaline electrolyte was composed of NaAlO212g/L,NaOH 4g/L,KaF 15g/L.Current density,process time and duty ratio were used to characterize the impact on thickness,corrosion resistant and wear resistance performance of MAO film.Simultaneously,the thermodynamic process and current-voltage relationship were also investigated.The impact of post-processing on MAO film composition and properties was preliminarily presented.Main work lists as follows:1.Microstructure and composition of MAO films were characterized by SEM and XRD,demonstrated that the porous 2-layer-MAO film was consist of MgO and MgAl2O4.The MAO voltage increased with the growth of current density.Towards a single sample,the growth rate reduced with the growth of time.The arc voltage approximated to 165V.2.The film thickness was tested by Coating Thickness Gauge,and the result shows that the thicknesses of MAO films increase with the growth of time and current density respectively.3.Effect of MAO processing parameters on film’s anti-corrosion properties was studied by using the electrochemical method of polarization curve.The results indicated that MAO-treatment improves the corrosion resistance of magnesium alloys.The corrosion resistance of the films reinforced at first then declined with the growth of time,current density and duty ratio.Parameters of corrosion current and polarization resistance were used to evaluate the anti-corrosion property of MAO film,which indicated that the best electrical parameters of MAO was current density 120mA·cm2,duty radio 20%and treating time 25 minutes.4.Impact of MAO processing parameters on film’s wear resistance property were investigated.The friction coefficient of MAO-treated magnesium alloys enhanced with time,current density and duty radio respectively under lubricated condition.The principles of corrosion wear changed by the alteration of load.5.Microstructure,composition and forming mechanism of different MAO-after-treatment methods were contrasted.The methods included hole-sealing and coating.The neutral salt immersion test and electrochemical analysis demonstrated that MAO-after-treatment enhanced the corrosion resistance of magnesium alloys.