Effects of Micro-arc Oxidation Process Parameters on Micro-structure and Properties of Al2O3 Coatings Prepared on Sintered 2024 Aluminum Alloy

In this work, Al2O3 ceramic coatings were prepared the surface of powder metallurgy (PM) 2024 aluminum alloy via the micro-arc oxidation (MAO) technique. The effects of the current density and the oxidation treatment time on the microstructure and properties of the MAO coatings were investigated. The results reveal that the oxide film mainly comprises the γ-Al2O3 phase, the amorphous Al2O3 phase, and a small amount of the mullite phase. There are traces of W in the coatings, which exist in the form of W, WO3, and W18O49. With increasing current density, the thickness and surface roughness of the MAO coatings prepared on the PM 2024 alloy increase, while their surface hardness first increases and then decreases. The increase in the current density promotes the transformation of the amorphous Al2O3 phase into the γ-Al2O3 phase. The maximum hardness value of 1270 HV is obtained at a current density of 20 A dm−2. The MAO coatings provide superior corrosion protection for the PM 2024 aluminum alloy, and the MAO coatings obtained at a current density of 15 A dm−2 exhibit the highest corrosion resistance.