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.