PSI - Issue 28

Dimitris Georgoulis et al. / Procedia Structural Integrity 28 (2020) 2297–2303 Author name / Structural Integrity Procedia 00 (2019) 000–000

2302

6

3.3.3. Elongation at fracture The values of the elongation at fracture A f of the pre-corroded tensile specimens can be seen in Fig. 5 (the same notation and interpolation approach as in Fig. 3 is followed) for both aluminium alloys studied in the present work. It can be seen from this figure that AA2198-T8 is more corrosion resistant than AA2024-T3 in terms of A f degradation at the first stages of corrosion exposure and up to 70 h (short exposure times regime) where the hydrogen embrittlement is the dominant degradation mechanism. It is worth mentioning that AA2198-T8 is superior to corrosion resistance even at the T8 condition (under-ageing) which leads to significant loss of ductility. However, almost the same degradation of elongation at fracture was noticed for the two investigated materials at long exposure times where pitting corrosion and cracking formation are the dominant degradation mechanisms. Hence, the AA2024-T3 specimens are losing their ductility potential at higher rates than AA2198-T8 giving evidence that Al-Cu-Li alloy is more corrosion resistant than its predecessor, in terms of highly maintaining its ductility characteristics when compared to the Al-Cu alloy for the same exposure time.

10 12 14 16 18 20 22

Aluminum alloys (AA) t = 3.2 mm, L rolling direction Exposure to 3.5 wt. % NaCl solution x.x% remaining mechanical property

100 %

83.9 %

long exposure times

69.5 %

100 %

65.2 %

2024-T3

92%

93.7%

0 2 4 6 8

22.9 %

29.6 %

2198-T8

Elongation at fracture [-]

37.3 %

short exposure times

11 %

0

1000 2000 3000 4000 5000

Exposure time to 3.5 wt. % NaCl solution [hours]

Fig. 5: Elongation at fracture degradation of pre-corroded AA2024-T3 and AA2198-T8 specimens exposed for different times to 3.5 wt. % NaCl solution. 4. Conclusions The tensile mechanical behaviour of two aluminium alloys was experimentally studied. The specimens were pre corroded in 3.5 wt. % NaCl solution for different exposure times. It was clearly noticed that corrosion degrades all aspects of the tensile behaviour of AA2024-T3 alloy at a higher level compared to the respective degradation of the tensile properties of the AA2198-T8 alloy at long exposure times where the pitting corrosion mechanism takes place. Regarding the elongation at fracture, AA2024-T3 was found to degrade at much higher rates even at the short exposure times where hydrogen embrittlement is the dominant degradation mechanism. It was thus definitely concluded that Al-Cu-Li alloy is superior concerning corrosion resistance, since it maintains higher percentages of the initial (uncorroded) values of its tensile properties, against AA2024. Acknowledgements The authors would like to thank Constellium and HAI for the provision of the materials. References

Alexopoulos, N.D., Siskou, N., Charalampidou, C. M., Kourkoulis, S.K., 2019.Simulation of the corrosion-induced damage on the aluminum alloy 2024 specimens with equivalent surface notches. Frattura ed Integrità Strutturale 50, 342-353.