Preparation of silicate tungsten bronzes on aluminum by plasma electrolytic oxidation process in 12-tungstosilicic acid

► Percentage of oxide coatings area covered by active discharge sites decreases with time. ► Spatial density of microdischarges is the highest in the early stage of PEO process. ► Oxide coating is partly crystallized and mainly composed of γ-Al2O3 and WO3. ► Outer layer of the coating is silicate tungsten bronze.