Effects of cerous nitrateadditive on microstructure and properties of MAO coatings on AZ91D magnesium alloy
In order to further improve the wear resistance and corrosion resistanceof AZ91D magnesium alloy,the ceramic coating was in-situ formed on AZ91D magnesium alloy by applying micro-arc oxidation(MAO)technique in the silicate electrolytic liquid system with different concentrations of cerous nitrateadditive.The phase composition and surface microstructure of the coatings were characterized by X-ray diffractometer(XRD)and scanning electron microscopy(SEM).The corrosion resistance and wear resistance of the ceramic coatings were evaluated by electrochemical tests and friction and wear tests.The results show that the addition of cerous nitrate is of little effect on the phase composition of the ceramic film.With the increase of the concentration of cerous nitrate,the surface of the coating first appeared larger pores,and then the number of pores decreased,and the pore size became smaller.Compared with the MAO coating without additive,when the concentration of cerous nitrate is 0.4 g/L,the wear time increases from 1min to 8 min,and the wear resistance is improved.Its corrosion potential increases from-1.69 V to-1.26 V,and the corrosion current density is reduced from 8.56×10-6 A·cm-2 to 2.49×10-7 A·cm-2,thus the corrosion resistance is significantly increased.