Characterization of aluminum anodized layers modified in sulfuric and phosphoric acid baths and their effect on conventional electrolytic coloring

Modification of anodic aluminum oxides induces light interference leading to various tunes of color after electrolytic coloring process. In this research, nano-morphology of an anodic aluminum oxide was modified via two procedures in sulfuric and phosphoric acid baths. The metallurgical changes after the modifications were evaluated and compared with unmodified conventional layer. Layer thickness, crystalline structure, surface topography and morphology, mechanical characteristics including elastic modulus and nanohardness, corrosion behavior and electronic properties of the oxide layer were evaluated. From the overall view, the modification had some destructive effects on corrosion performance and mechanical properties of the anodized layers. The aluminum oxide layer was characterized as an n-type semiconductor and the modification increased its conductivity. The effects of the oxide modification on creating interference colors using the electrolytic coloring method were evaluated. The electrolytic coloring generated brown color on the oxide layer modified in the sulfuric acid bath. Conversely, a green interference color was obtained for the oxide layer modified in the phosphoric acid bath.