Investigation of an environmentally friendly coloring coating for magnesium-lithium alloy micro-arc oxidation

Abstract

An environmentally friendly coloring coating of magnesium-lithium alloy micro-arc oxidation is proposed, with excellent corrosion resistance and optical camouflage protection functionality. Through formula design and process optimization, the coating was been successfully formed on Mg-8Li-1Al alloy using a specially-developed micro-arc oxidation pilot line. The influence of process parameters on the color and properties of the coating was investigated. The results show that the coating prepared with the electrolyte system, in dark green color, consisted of silicate as the base electrolyte and copper sulfate as the colorant, has an excellent apparent quality. As process parameters, current density and coating's duration have significant effects on the color and properties of the coatings - increasing either or both will lead to the deepening of the color and the increase of the thickness and hardness of the coloring coatings. With current density of 20 mA/cm2 and coating's duration of 10 min, the coloring coating prepared using the power supply with constant current exhibits superior corrosion resistance, with the surface roughness to the national standard level Ra 0.8 μm, the salt spray corrosion resistance to the national standard level 9 and the microhardness 179% higher than that of substrate.