Microstructure of alumina layers formed by PEO with PEG additive

This study addresses a knowledge gap by providing depth-resolved analysis of the phase compositions and crystallite sizes within surface layers formed by plasma electrolytic oxidation (PEO) on AlMg3 (EN AW-5754) alloy while comparing effects of different amounts of Polyethylene Glycol (PEG) additive. Structural characterization includes Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), 3D surface contour scans and Grazing Incidence X-ray Diffraction (GIXRD). Crystallographic investigations reveal a compositional gradient in the coating containing both η -Al 2 O 3 and metallic Al, while PEG addition leads to smaller crystallites in the η -Al 2 O 3 phase. TEM investigations confirm the presence of both η -Al 2 O 3 and metallic Al within the layer. Cross-sectional analyses display a clear interface between the substrate and coating. Surface morphology changes were observed, indicating a reduction of surface roughness induced by the additive, which is accompanied by increased layer thickness uniformity and reduced porosity. PEG’s potential in fine-tuning the oxide layer’s morphology and microstructure to reduce roughness while improving homogeneity and maintaining a crystalline Al 2 O 3 layer is demonstrated.