Structural and Phase State and Mechanical Properties of PEO Coatings on Al–Si Alloys with Al2O3 and SiO2 Nanoparticles

Abstract

This paper presents the results of a comprehensive investigation of the structural, phase, and mechanical properties of plasma electrolytic oxidation (PEO) coatings formed on the surface of EN AC-45000 (AlSi6Cu4) aluminium–silicon alloy in an electrolyte containing Al2O3 and SiO2 nanoparticles. The aim of the study was to determine the effect of electrolyte nanomodification on the morphology, phase composition, and microhardness of PEO coatings. The PEO process was carried out in a NaOH-based aqueous electrolyte with the addition of aluminium and silicon oxide nanoparticles. The microstructure and morphology of the coatings were investigated using optical and scanning electron microscopy. The elemental and phase compo sition was determined by energy-dispersive analysis and X-ray diffraction. The mechanical properties were evaluated by measuring the microhardness using the Vickers method, while the tribological performance was assessed using the ball-on-disk method under dry sliding conditions. The results showed that a two-layer ox ide coating was formed on the alloy surface, consisting of a dense inner α-Al2O3 barrier layer and a porous outer layer predominantly composed of γ-Al2O3. The incorporation of nanoparticles contributed to coating densification, reduced porosity, and promoted a more uniform distribution of micro-arc discharges. After PEO treatment, the surface microhardness increased from 65–80 HV to approximately 245–250 HV, repre senting more than a threefold increase. The coatings also exhibited a stable tribological response, character ized by a higher yet stable coefficient of friction and improved wear resistance compared to the untreated al loy. These results demonstrate the high potential of nanomodified PEO for enhancing the operational perfor mance of aluminium–silicon alloys.