2026 AZ31 Black Micro Arc Oxidation Coating

Magnesium alloys require protective surface coatings for widespread application, with micro-arc oxidation (MAO) being a prominent technique. However, conventional MAO coatings are typically gray or light-colored, necessitating secondary treatments for specific colors like black, which complicates the process. This study aims to develop a one-step method for fabricating black MAO coatings on AZ31 magnesium alloy by introducing cupric pyrophosphate (Cu2P2O7) as a colorant into a silicate-based electrolyte. As the Cu2P2O7 concentration increased from 0 to 5 g/L, the coating color transitioned from grayish-white to pink, then brownish-black, achieving a uniform black appearance at 4–5 g/L. XPS and EDS analyses confirmed the incorporation of copper as CuO, indicating that the addition of Cu2P2O7 not only altered the color but also influenced the coating's structural properties. The optimal concentration resulted in enhanced coating density by thickening the dense layer and decreasing pore size. This one-step preparation process simplifies the surface treatment of magnesium alloys and may facilitate applications in various fields including aerospace and automotive, providing aesthetically pleasing and functional colored surfaces.