Effect of TiO_2 nanoparticles on the microstructure and corrosion behavior of MAO coatings on magnesium alloy

摘要

The microstructure and corrosion behavior of the micro-arc oxidation (MAO) coatings modified by TiO_2 on AZ91 magnesium alloys were investigated by SEM, EDS, XRD, electrochemical analysis and drop test, respectively. The modified MAO coatings were consisted of not only MgAl_2O_4 and MgO, which usually could be found in MAO coatings on the AZ91 alloys, but also a small quantity of Ti. With increasing the contents of TiO_2 nanoparticles from 0 to 4.8 g/L in the electrolyte, the coatings thickness increased from 19 to 24μm, and the color of the MAO coating changed from light gray to dark. The addition of TiO_2 could effectively decrease the number of the pores and improve the density of the coatings. The corrosion potential of the modified coatings positively shifted about 180 mV and the corrosion current density declined and the drop time increased. The mechanism of the corrosion resistances of the modified coatings lay in the fact that TiO_2 nanoparticles could increase the thickness and the density of the coatings on the AZ91 magnesium alloys.