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

In this work, Al 2 O 3 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-Al 2 O 3 phase, the amorphous Al 2 O 3 phase, and a small amount of the mullite phase. There are traces of W in the coatings, which exist in the form of W, WO 3 , and W 18 O 49 . 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 Al 2 O 3 phase into the γ-Al 2 O 3 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.