PSI - Issue 28

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

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squares, is not significantly affected by corrosion for short exposure times up to 720 h where the remaining percentage of the conventional yield stress is approximately 99%. However, a significant decrease is noticed for long exposure times (> 1000 h) where the remaining percentage of the initial property value is almost 69 % after the highest exposure time of 4320 h in this case. AA2198-T8 exhibited slightly higher conventional yield stress degradation (up to 4 % from the initial property value) than AA2024-T3 for short exposure times. Nevertheless, in contrary to AA2024-T3 further corrosion exposure of AA2198-T8 seems to not affect the mechanical property since the remaining percentage remains constant even after heavily exposure specimens (black triangles in Fig. 3).

550

long exposure times

2198-T8

500

100 %

96 % 97.9 %

96 %

96.5 %

0 200 Conventional yield stress R p0.2% [MPa] short exposure times 250 300 350 400 450 99.6 % 99.4 % 100 %

2024-T3

98.9 %

92.7 %

68.5 %

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

0

1000 2000 3000 4000 5000

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

Fig. 3: Conventional yield stress degradation of pre-corroded AA2024-T3 and AA2198-T8 specimens exposed for different times to 3.5 wt. % NaCl solution.

3.3.2. Tensile strength The values of the tensile strength R m were again calculated by taking into account the nominal cross-sections of the specimens and the results are summarized in Fig. 4. Comparative consideration of the plots for the two investigated aluminium alloys shows that AA2198-T8 degrades at slightly higher rates in comparison to AA2024-T3 regarding the short exposure times, e.g. 96 % remaining percentage of R m was noticed after 720 h of exposure while the respective value of AA2024-T3 was approximately 99 %. On the contrary, long exposure times have a profound effect on AA2024-T3 where the remaining percentage of the initial property decreased to 86 % while for AA2198-T8 the respective degradation was approximately 90 %.

600

long exposure times

550

100 %

2198-T8

96.8 %

95.8 %

350 Ultimate tensile strength R m [MPa] 400 450 500 99.2 % short exposure times

93.2 %

98.2 % 98.5 % 100 %

89.2 %

86 %

85.3 %

2024-T3

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

0 300

0

1000 2000 3000 4000

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

Fig. 4: Ultimate tensile strength degradation of pre-corroded AA2024-T3 and AA2198-T8 specimens exposed for different times to 3.5 wt. % NaCl solution.