Investigation of the Addition of (NaPO₃)₆ to Al₂O₃ Ceramic Coatings Prepared on AlSi10Mg Selective Laser Melted Components via Micro-Arc Oxidation

Al₂O₃ ceramic coatings were prepared on the surface of AlSi10Mg selective laser-melted components via micro-arc oxidation. The microstructure and corrosion property of the coatings were investigated. Scanning-electron microscopy results indicated that the number of “craters” on the coatings’ surface increased with selective laser-melted energy density. The surface of the coatings became smooth with an increase in (NaPO₃)₆ content, and the number of “craters” decreased. X-ray diffraction and x-ray photoelectron spectroscopy results showed that the coatings were composed of γ-Al₂O₃ and α-Al₂O₃. In particular, γ-Al₂O₃ content increased and α-Al₂O₃ appeared, surface roughness decreased from 2.22 μm to 1.21 μm. Meanwhile, corrosion current density decreased from 3.46e⁻⁰⁰⁶ to 9.71e⁻⁰⁰⁷ A cm⁻² and the corrosion depth decreased from 4.62e⁻⁰⁴ to 1.09e⁻⁰⁵ mm/year. The morphologies of the coatings were influenced by the diameter of keyholes. The small keyholes were enclosed, and the inside of large keyholes formed micro-arc oxidation coatings. The addition of (NaPO₃)₆ increased the threshold value for obtaining consistent coatings.