Microstructure and Its Effect on the Intergranular Corrosion Properties of 2024-T3 Aluminum Alloy

Abstract

Intergranular corrosion is the main corrosion type of Al-Cu-Mg aluminum alloys, which seriously reduce the lifetime of aircraft structural parts. In this paper, the microstructure and the intergranular corrosion behavior of 2024 alloy with varying Cu and Mg content were studied by using a scanning electron microscope (SEM), transmission electron microscope (TEM), and three-dimensional atom probe (3DAP). The results show that nano-scale θ (Al2Cu) and S (Al2CuMg) particles precipitate along grain boundaries after quenching. The nano-cluster is the main strengthening phase in the 2024 alloy after natural aging for 96 h. The intergranular corrosion susceptibility is greatly affected by the presence of θ (Al2Cu) and S (Al2CuMg) phases along grain boundaries. Specifically, Cu-rich precipitates and intermetallics are known to act as local cathodes, which facilitates the action of oxygen reduction and ultimately drives anodic dissolution of the surrounding matrix material. The intergranular corrosion resistance of the alloy decreases with the increase in Cu and Mg contents. The alloy with a lower Mg content shows better corrosion resistance than the commonly used one with a Cu to Mg mass ratio of 2.9. The relationship between the observed corrosion behavior and various contents of Cu and Mg elements is discussed, which has potential to benefit the composition design of 2xxx aluminum alloy with high corrosion resistance.

Protection of AA2024 alloy against wear and corrosion by HVAF sprayed AlCuFe coating

“…Second, the coating comprises the relatively homogeneous mixture of two phases of different mechanical properties forming some kind of armoured material (Figure 3(e)): ψ-phase possesses a higher hardness while the β-phase is characterized by slightly lower hardness and better plasticity (indicated by arrows). This feature seems to promote load partitioning and timely relaxation in the coating surface layer tested, which results in better wear/friction behaviour [25][26][27][28][29][30][31]47,48]. Additionally, the porosity of the coating surface (Figure 3(d,e)), which facilitates better lubrication by the liquid paraffin, also promotes better wear resistance and lower CoF.…”

“…Nonetheless, the coatings are seen to effectively protect the AA2024 alloy (Figure 4 Generally, materials with more negative E cor are known to experience more significant corrosion damage and vice versa. Corrosion current density i cor is also indicative characteristic of the degree of the material degradation at corrosion attack [33,35,36,39,[45][46][47][48][49]. In this study, the i cor values were assessed using a Tafel fitting by the intersection of the tangent to cathodic polarization curve and the E cor level [39,44].…”

Comparative Study of Techniques and Methods Used to Characterize Intergranular Corrosion in AA2024 Aluminum Alloy

“…Al 2 CuMg and Al-Cu-Mn-Fe IMPs, in agreement with the literature. 3,7,[9][10][11][12] For reasons of confidentiality, no accurate information on the nature of the protection systems used is given in the manuscript. The 1 mm thick plates were protected by hexavalent chromium conversion coating with epoxy primer containing strontium chromate inhibitor and electrophoretic paint, while tartaric sulfuric anodizing without chromate primer and chromic acid anodizing with epoxy primer containing strontium chromate inhibitor were used for the 8 mm thick plates.…”

“…Moreover, the formation of a precipitate-free zone (PFZ) surrounding the grain boundaries has been shown to increase the IGC susceptibility. 3,7,[9][10][11][12] However, even in the absence of precipitates at the grain boundaries, IGC can be observed. 12,13 Indeed, one should not forget the influence of other microstructural parameters on IGC susceptibility, e.g.…”

Effect of Exfoliation Corrosion on the Mechanical Properties of Friction Stir Spot Welded 2024-T3 AA Joints

“…Tey act as crack initiation sites in addition to reduce the contact area between the upper and lower sheets. Boag et al [29] and Xiao et al [30] reported a dissolution of the cathodic intermetallic phase due to pitting corrosion on these particles themselves. Increasing the exposure time to 30 h, the tensile shear load showed a continuous reduction down to 1.8 kN (0.04 kN/h.…”