Corrosion protection of AA 2024-T3 by bis-[3-(triethoxysilyl)propyl]tetrasulfide in neutral sodium chloride solution. Part 1: corrosion of AA 2024-T3

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

“…The EDX O map exhibits the deposition of corrosion products in the periphery of the second phase particle, indicating that attack is concentrated at the intermetallic/matrix interface, resulting in the dissolution of the Al alloy close to the intermetallic. Consequently, in agreement with previous work, the SEM and Auger/EDX results show that the Al-Cu-Fe-Mn intermetallic is cathodic with respect to the matrix [3][4][5].…”

“…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.…”

“…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.…”