Microstructure, Hardness, and Corrosion Behavior of Oxidized AA6061 Using Potentiostatic Plasma Electrolytic Oxidation

Aluminum and its alloys are widely used in aerospace and industrial sectors due to their high specific strength, low density, and abundance. However, their low hardness, high corrosion susceptibility, and poor wear resistance limit broader applications. Surface treatments such as electroplating, PVD/CVD, and anodizing have been used to enhance surface properties. Plasma electrolytic oxidation (PEO), also known as micro-arc oxidation (MAO), has emerged as a promising technique for producing durable ceramic coatings on light metals like Al, Mg, and Ti alloys. In this study, PEO was applied to AA6061 aluminum alloy using an AC power source in potentiostatic mode at 350 V and 400 V, 1000 Hz, and 80% duty cycle for 30 min in a silicate-based electrolyte (5 g/L Na2SiO3 + 5 g/L KOH) maintained at 25–40 °C. The effect of voltage on the coating morphology, thickness, and corrosion resistance was investigated. The coatings exhibited porous structures with pancake-like, crater, and nodular features, and thicknesses ranged from 0.053 to 83.64 µm. XRD analysis confirmed the presence of Al, α-Al2O3, Ƴ-Al2O3, and mullite. The 400 V-coated sample showed superior corrosion resistance ( Ecorr= −0.77 V; icorr=0.28 μA/cm2) and improved hardness (up to 233 HV), compared to 89 HV for the bare AA6061.