Effect of Alloy Composition on Pore-widening Induced Structural Evolution and Wettability of Anodic Aluminum Oxide

Anodic aluminum oxide (AAO) is commonly utilized in functional surface engineering, yet the influence of alloy composition on AAO growth behavior, pore-widening (PW) characteristics, and structural stabil- ity remains poorly understood. This study investigates AAO films formed on Al 1050, Al 3003, Al 5052, and Al 6061 through anodization for 1 hour under identical conditions, followed by PW in phosphoric acid for varying durations. Despite the same anodizing conditions, significant differences were noted in pore diameter, oxide-film thickness, and AAO growth rates based on alloy composition. Al 5052 demonstrated the highest growth and PW rates, while Al 3003 exhibited the lowest. During the PW process, all alloys ini- tially experienced increased porosity and enhanced wettability; however, extended PW led to distinct collapse behaviors of the oxide film that were dependent on the alloy. These behaviors ranged from gradual structural transformation to rapid oxide removal. Notably, wettability enhancement occurred only while a stable porous structure was intact; once the oxide film collapsed or was removed, wettability reverted. These findings indicate that the PW rate and structural stability are governed by different mechanisms, highlighting the critical role of alloy composition in influencing AAO growth, collapse behavior, and wettability.