Anodization of arc-sprayed Al and Al–Mg coatings on super duplex stainless steel: Structural evolution, corrosion, and tribocorrosion performance

Super duplex stainless steel was coated with pure aluminum and Al–5Mg using the electric arc spraying technique, followed by anodization under identical conditions to produce nanotubular Al2O3 films. The structural and morphological features of the coatings were examined using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy coupled with energy-dispersive elemental analysis, and microhardness measurements. The electrochemical behavior was evaluated in synthetic seawater by means of potentiodynamic polarization and electrochemical impedance spectroscopy, while tribocorrosion performance was assessed under reciprocating sliding conditions. Mg incorporation increased pore diameter and modified the oxide crystal structure, as confirmed by XRD peak shifts. Although anodization improved hardness, corrosion resistance, and tribocorrosion performance for both systems, the pure Al coating with finer nanotubular morphology exhibited the highest hardness and corrosion resistance compared to the anodized Al–5Mg coating. This improvement is attributed to the formation of a compact anodic Al2O3 nanotubular layer with refined pore morphology, which enhances barrier effectiveness against electrolyte penetration and increases surface load-bearing capacity, whereas Mg incorporation leads to pore enlargement and reduced oxide compactness. These findings demonstrate that controlled alloying and anodization of arc-sprayed coatings provide an effective strategy for tailoring oxide morphology and enhancing protective performance in marine environments.