PSI - Issue 42

5

Christina Margaraita Charalampidou et al. / Procedia Structural Integrity 42 (2022) 1708–1713 Charalampidou et al./ Structural Integrity Procedia 00 (0000) 000 – 000

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3.3 Effect on the mechanical properties Fig. 3a shows the experimental results of conventional yield stress R p0.2% of AA2198-T8 exposed to three different corrosive solutions as average values and respective standard deviation derived from three different specimens of each case. The results revealed higher degradation of R p0.2% for the specimens exposed to EXCO solution (represented with the purple curve and linked to the upper tick label scale) for the whole exposure time range, when compared against the other two investigated solutions. A sudden stress drop was noticed after 12 h of exposure to EXCO solution, that is probably attributed to the increase of micro-cracks depth, while further corrosion exposure did not affect the conventional yield stress significantly. This can be probably attributed to the maximum depth of attack achieved as also mentioned in Alexopoulos and Papanikos (2008). Specimens exposed to NaCl solution exhibited only a slight decrease (approximately 2 %) of conventional yield stress up to 720 h of exposure and afterwards the residual R p0.2% values were stabilized for additional exposure times. Finally, for the case of Harrison’s solution , no stress drop was noticed up to 720 h and further corrosion exposure led to slight decrease of R p0.2% , e.g., approximately 6 % after the 4320 h. Regarding elongation at fracture A f shown in Fig. 3b, corrosion behaviour of the three different solutions was different from the respective of conventional yield stress. In this case, specimens exposed to EXCO solution showed higher corrosion resistance by means of higher remaining percentage (approximately 65 % after 48 h of exposure) as well as degradation rate of A f . However, for the very short exposure times where pitting corrosion is limited specimens exposed to NaCl solution revealed slightly higher corrosion resistance than specimens exposed to EXCO. After 720 h specimens exposed to NaCl solution exhibited essential degradation of elongation at fracture that almost reached the respective of Harrison solution.

Exposure time to corrosion solution [Hours]

Exposure time to corrosion solution [Hours]

0

10

20

30

40

50

0

10

20

30

40

50

10 12 14 16 18 20 22 Elongation at fracture A f [%] 97% 98% 100% 94%

500

AA2198-T8, t = 3.2 mm L rolling direction Exposure to corrosion solutions x.x% remaining percentage from the initial value

480

3.5 % NaCl

100%

99.8%

99.9%

98.3%

97.6%

460

380 Conventional yield stress R p0.2% [MPa] 99.1% 91% EXCO 400 420 440

98%

95.9%

EXCO

Harrison's

93.6%

99%

85%

89.4%

90% 80%

88.7%

0 2 4 6 8

89%

86.3%

70%

65%

3.5 % NaCl

AA2198-T8, t = 3.2 mm L rolling direction Exposure to corrosion solutions x.x% remaining percentage from the initial value

34%

Harrison's

16%

18%

12%

0

0

1000 2000 3000 4000 5000 Exposure time to corrosion solution [Hours]

0

1000

2000

3000

4000

5000

Exposure time to corrosion solution [Hours]

(a)

(b)

Fig. 3: Comparison of experimental results of (a) conventional yield stress R p0.2% and (b) elongation at fracture A f of AA2198-T8 exposed to three different corrosive solutions. 4. Conclusions In the present work the corrosion mechanism of AA2198-T8 as well as the corrosion-induced degradation on the mechanical properties were investigated. Three different corrosive environments of various aggressiveness were used to examine all possible corrosion mechanisms. The experimental results showed that specimens exposed to EXCO solution exhibited higher degradation of conventional yield stress due to micro-cracks depth evolution. However, severe localized corrosion attack noticed in Harrison solution led to lower corrosion resistance in terms of elongation at fracture decrease.