Grain‐stored energy and the propagation of intergranular corrosion in AA2xxx aluminium alloys

Abstract

In the present study, intergranular corrosion (IGC) in AA2024 and AA2099 aluminium alloys was investigated. The IGC propagation path was examined using scanning and transmission electron microscopies. Further, electron backscatter diffraction was employed to investigate the relationship between the grain structure and the IGC susceptibility. It was found that IGC could occur at grain boundaries where second phase precipitates were absent. It was also revealed that IGC occurred at the grain boundaries that surround grains of relatively high-stored energy, and corrosion was not confined within the region immediately adjacent to the grain boundaries but had developed into the grains of relatively high-stored energy, suggesting that IGC propagated within the grains that have relatively high levels of defects.

Characterization of intergranular corrosion defects in a 2024 T351 aluminium alloy

“…In addition to the mechanism describing the Cu-rich interfacial layer growth, the presence of this layer puts into question the corrosion mechanism and the propagation kinetics of the intergranular corrosion defect in an AA2024. Some authors [7][8][9] explain that the Cu-enrichment could protect the interior of the grain from further corrosive environment in AA2024. Clearly, Cu could provide effective cathodic support [9] for oxygen and/or protons reduction on the walls of the intergranular corrosion defects.…”

“…Usually, these mechanisms are described as a gal vanic coupling between intergranular Cu-rich particles (0-Al i Cu; S-Al i CuMg) and the adjacent matrix (3)(4)(5)(6). However, some authors have shown that precipitate-free grain boundaries are also suscep tible to intergranular corrosion suggesting that other parameters as grain stored energy have to be taken into account (7,8).…”

“…Depending on the metallurgical state of the alloy, this can Jead to the formation of a precipitate free zone (PfZ) surrounding the grain boundaries and increasing the susceptibility to intergranular cor rosion of these alloys. The electrochemical characteristics of the Cu-rich intermetallic phases, and mainly S-AliCuMg, have been widely studied (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Authors assumed a mechanism based on the strong reactivity of the partiel es that led to a Cu-enrichment ail along the corroded grain boundaries when the alloy was exposed to an aggressive solution.…”

“…Authors assumed a mechanism based on the strong reactivity of the partiel es that led to a Cu-enrichment ail along the corroded grain boundaries when the alloy was exposed to an aggressive solution. Such a Cu-enrichment ail along the cor roded grain boundaries may have a strong effect on the progress and kinetics of the intergranular corrosion defects (7)(8)(9). There fore, it is of great interest to have an accurate description of the intergranular corrosion defects.…”

Influence of hydrogen on the propagation of intergranular corrosion defects in 2024 aluminium alloy

“…Further, previous studies showed the formation of a thin metallic Cu-nanoparticles layer at the interface alloy-IGC defect [20], that could be due to dissolution of the Cu-rich intergranular precipitates [19,21], and/or to the matrix dissolution [22]. This Cu-rich layer could protect the interior of the attacked grains from further corrosive environment in AA 2024 [19,23,24]. However, Cu could also provide effective cathodic support for oxygen and/or protons reduction on the walls of the IGC defects [24].…”