Alumina Formation on Pure Aluminum via PEO Process in Electrolytes with Different Silicate-Aluminate Ratios

This study systematically investigates the effect of electrolytes with varying silicate–aluminate ratios on the microstructure, phase composition, coating thickness, and surface roughness of aluminum coatings synthesized via the PEO process on pure Al. The coatings primarily consist of mullite (Al6Si2O13), ɣ-Al2O3 and α-Al2O3 phases. Increasing the aluminate content promoted α-Al2O3 formation and a higher number of smaller discharge channels, while higher silicate content favored mullite formation. Coating thickness increased with higher silicate concentrations, whereas surface roughness remained relatively constant across different electrolyte compositions.