A study on pitting corrosion of aluminum alloy 2024-T3 by scanning microreference electrode technique

Localized corrosion of a 2219 aluminium alloy exposed to a 3.5% NaCl solution

“…Considering the Auger data, the Al and O images are similar and indicate that, as expected, there is a general deposition of aluminium oxide based corrosion products as the exposure time increases. However, examination of the point analysis in Figure 6 shows that the Al/O intensity on the matrix shows no change as a function of exposure time, but on the intermetallic the Al/O intensity drops as the exposure time increases (probably due to the formation of other oxide based corrosion products in addition to Al(OH) 3 ). In contrast, the Fe, which prior to exposure exhibited a negligible intensity on the intermetallic, shows an increase in the Fe/O ratio as the exposure time increases.…”

“…The S phase precipitates are particularly susceptible to pitting corrosion [3,4]. Both Shao et al [3] and Zhu and van Oiij [4] found that initially these precipitates are anodic with respect to the matrix and rapid dealloying of Mg is observed. Later, attack occurs in the matrix at the Al alloy/precipitate interface [3,4], indicating that following this initial anodic dissolution, the change in composition results in the precipitates becoming cathodic with respect to the matrix.…”

“…The θ' is cathodic to the alloy matrix and causes corrosion of the Al alloy at the precipitate/alloy interface [1]. The S phase precipitates are particularly susceptible to pitting corrosion [3,4]. Both Shao et al [3] and Zhu and van Oiij [4] found that initially these precipitates are anodic with respect to the matrix and rapid dealloying of Mg is observed.…”

“…The major second phase precipitates in these alloys are Al-Cu-Fe-Mn, with a variable composition and size from 1 to 30 µm. Such Al-Cu-Fe-Mn second phase particles are generally accepted to be cathodic with respect to the matrix [3][4][5]. The corrosion behaviour of Al-Cu-Fe-Mn intermetallics has been the subject of several studies on the 2024 alloys, where the Al-Cu-Fe-Mn phase and the S phase have been found.…”

“…The corrosion behaviour of Al-Cu-Fe-Mn intermetallics has been the subject of several studies on the 2024 alloys, where the Al-Cu-Fe-Mn phase and the S phase have been found. Shao et al [3] observed significant pitting at the S phase sites but no observable corrosion activity on the Al-CuFe-Mn phase after 2h immersion in a 0.01 M NaCl solution. Zhu et al [4] immersed the alloy for 72 h in a 0.6 NaCl solution and reported heavy corrosion around the S phase particles, but minimal activity around the Al-Cu-Fe-Mn phase.…”