Microstructure and multi-scale mechanical behavior of hard anodized and plasma electrolytic oxidation (PEO) coatings on aluminum alloy 5052

The microstructural and mechanical features of the two leading electrolytic coating methods, hard anodizing and plasma electrolytic oxidation (PEO), on a 5052 aluminum alloy are investigated via extensive indentation and scratch testing along with accompanying characterization techniques. The hardness of the PEO coating (~ 12 GPa) was found to be approximately three times that of the hard anodized coating (~ 4 GPa). Indentation stress–strain curves were measured across the coating thickness. Both coatings were found to display greater adhesive strength than cohesive strength, so adhesion could not be measured by scratch testing. Micro-scratch resistance was found to scale similarly to hardness. Correlations between these mechanical performance measures and observed microstructures are discussed.