An assessment of pitting corrosion in anodized aluminum alloys: It might not be what it seems

• Published in: Materials and corrosion 2024-05, Vol.75 (5), p.599-613
• Main Authors: Sousa Araujo, João Victor, Milagre, Mariana Xavier, Zhou, Xiaorong, Costa, Isolda
• Format: Article
• Language: English
• Subjects: Aluminum base alloys; Aluminum oxide; Anodic polarization; Anodizing; Electrode polarization; image analysis; Magnesium; Optical microscopy; optical profilometer (OP); pit morphology; Pitting (corrosion); SEM (BSE‐SE); Sulfuric acid
• ISSN: 0947-5117; 1521-4176
• DOI: 10.1002/maco.202313977

In this study, special attention was given to the characterization of pits on the anodized aluminum alloy (Al–Zn–Mg–Cu) with an anodic aluminum oxide formed in tartaric sulfuric acid. Anodic polarization in 0.1 mol L−1 NaCl solution was used to initiate pitting corrosion in the anodized alloy. Pit characteristics, such as morphology and depth, were evaluated by using optical microscopy and optical profilometry, and scanning electron microscopy. The methodology adopted in this study revealed severe under‐film pitting due to highly occluded conditions and showed that the extent of the under‐film pitting is significantly greater than the size of pit mouth observed from the surface. The morphology and propagation of pitting corrosion on anodized aluminum alloy (Al–Zn–Mg–Cu) in tartaric sulfuric acid were investigated. It was observed that depending on the methodology used to assess the depth of the corrosive attack, misinterpretations can be obtained. Information about the corrosion attack depth was discussed. This information is of great importance for evaluating pitting corrosion in Al alloys.