Nanoscale corrosion investigation of surface nanocrystallized 7150 Al alloy in 3.5 wt% NaCl solution by using FIB-TEM techniques

Corrosion property of Al alloys subjected to surface severe plastic deformation: a review

“…Sun et al (2022d) reported that the pitting potential of AA7075 alloy shifted to a more positive direction after USRP, indicating an improved resistance to pitting corrosion initiation. Figure 4(a)–(b) show the corrosion morphologies of cross section of the peened 7150 Al alloy after immersing into 3.5 Wt.% NaCl solution at room temperature for 6 h (Sun et al , 2022a). By comparing the near peened surface area [Figure 4(a)] and the peening-unaffected substrate area [Figure 4(b)], we can see that pitting corrosion is much less pronounced in the topmost ∼150 µm thickness layer than in the unaffected substrate area.…”

“…Given the importance of IGC for aircraft Al alloys, our group systematically investigate the role of surface nanocrystallization on IGC behavior for several alloys including AA7150 (Sun et al , 2022a; Sun et al , 2018a), AA7034 (Liu et al , 2023), AA7055 and AA2024 (Sun et al , 2018b). IGC was completely inhibited in both AA7150-ND and AA7150-TD samples, as shown in Figure 5 (Sun et al , 2020).…”

“…By comparing the near peened surface area [Figure 4(a)] and the peening-unaffected substrate area [Figure 4(b)], we can see that pitting corrosion is much less pronounced in the topmost ∼150 µm thickness layer than in the unaffected substrate area. Actually, the SP affected thickness was determined as ∼150 µm, presenting a very good relationship between the altered microstructure and the property (Sun et al , 2022a). Figure 4(c)–(d) shows the immersion corrosion test results of Al–2Mn alloys without [Figure 4(c)] and with [Figure 4(d)] S 2 PD treatment (Sun et al , 2022c).…”

“…The formation of equiaxed nanograins on surface layer has dual effects, which is it significantly enhanced pit initiation resistance but accelerated propagation kinetics. IGC of ultrasonic shot peened AA7150 in 3.5 Wt.% NaCl solution was further studied by combining focused ion beam and transmission electron microscopy techniques (Sun et al , 2022a). Nanoscale corrosion investigation indicates that, in 3.5 Wt.% NaCl solution, compared with the untreated substrate alloy, IGC is eliminated on the surface nanocrystallized layer.…”

“…Nanoscale corrosion investigation indicates that, in 3.5 Wt.% NaCl solution, compared with the untreated substrate alloy, IGC is eliminated on the surface nanocrystallized layer. The transition from IGC to uniform corrosion caused by ultrasonic SP can be attributed to the disappearance of PFZ along grain boundaries (Figure 6; Sun et al , 2022a). In addition, for the purpose of further illustrating the initiation and propagation mechanisms of pits with different shapes tuned by USSP, it is very important to obtain the spatial distribution of H + , Cl − , Al 3+ and other species inside/around the pits.…”