Investigations on the thermal control properties and corrosion resistance of MAO coatings prepared on Mg-5Y-7Gd-1Nd-0.5Zr alloy

Abstract

In this paper, the micro arc oxidation (MAO) method was utilized to prepare the ceramic coatings on Mg-5Y-7Gd-1Nd-0.5Zr substrate. Effects of different reaction time and NH4VO3 concentration on the morphology, composition, absorptance, emissivity, corrosion resistance and adhesion strength of coatings were investigated. These results show that the as-prepared coatings were mainly composed of Mg, Si, P, V, O and Na elements, and all of them existed as amorphous state. With the increases of reaction time and NH4VO3 concentration could improve the thickness, roughness and reduce the lightness (L value), and so the absorptance and emissivity of prepared coatings increased. Meanwhile, the corrosion resistance of coatings was much better than that of Mg alloy, exhibiting an increasing tendency as the reaction time and NH4VO3 concentration. However, too more NH4VO3 might cause many pores and micro-cracks generated on the surface of coatings, which slightly reduced the corrosion resistance. Although scratch tests denote that the adhesion strength of coatings decreased with the increase of thickness, T4/N4 with the maximum thickness still had good adhesion to the substrate and remained stable after thermal shock experiments. In general, T4/N4 possessed the optimal comprehensive performances, which would expand the application range of Mg-5Y-7Gd-1Nd-0.5Zr in aerospace and optics.