Microstructure and Corrosion Behavior of PEO-Coated AA7075 Under Pulsed Unipolar Potential Control Mode

Plasma electrolytic oxidation (PEO) has emerged as a promising surface coating technique producing high-quality ceramic coating for light metals like Al, Mg, Ti, and their alloys. AA7075 is one of the commonly used Al alloys for aircraft structures, gears and shafts, and automotives as it provides high yield and tensile strength. However, Al and its alloys have drawbacks that limit their further application. Thus, surface treatments are proposed to improve the metal and its alloy’s properties. In this study, the PEO of AA7075 was carried out with an AC power source under a pulsed unipolar potentiostatic mode at varying voltages of 425 and 450 V in 1000 Hz and at 80% duty cycles of 30 m. The effect of varying voltages on the morphology, coating thickness, and corrosion resistance of the PEO-coated samples was investigated. Surface morphology, elemental distribution, and phase composition were characterized using SEM, EDX, and XRD. A porous structure with a pancake-like shape, a crater, and nodular structures were observed with coating thickness ranges from 12.1 to 55.3 ± 4.67 µm. Al, α-alumina, and γ-alumina were detected in all surface coatings. The PEO-coated sample at 450 V exhibited higher corrosion resistance evaluated via potentiodynamic polarization and EIS.