PSI - Issue 37

Dimitris Georgoulis et al. / Procedia Structural Integrity 37 (2022) 941–947 Georgoulis et al. / Structural Integrity Procedia 00 (2021) 000 – 000

946 6

Table 1. The fitted values of the circuit elements in the equivalent circuit.

Corrosion exposure time of 2198-T3 / 2198-T8

Parameters R1 ( Ω *cm 2 ) Error (%) R2 ( Ω *cm 2 ) Error (%)

5 min

1 h

3 h

6 h

12 h

24 h

48 h

41.97 1.144

37.73 1.271

44.52 1.342

38.63 1.104

42.64 1.998

38.015 40.82

37.13 41.94 38.72 41.87

40.44 43.5

40.8 1.018 5665 3.041 9.959 3.262 0.973 1.951 20.84 22.56 9.539 1.548 4.363 0.740 1.606 5.702

0.454

1.465

0.729

1.105 7825 2.467

0.885 5090

1.514 7040 2.143

1.038 6700 2.795

1.568 9465 2.125

53900 22245 48305 27865 29385 20190

17300 7500

1.243

1.491

1.498

1.392

1.875

0.570

1.665

0.840

3.709

Q1 ( μΤ ) Error (%)

0.733 1.732 0.894 0.261

2.149 2.234 0.853

1.266 2.101 0.870 0.344

2.534 1.874 0.850 0.325

1.621 3.184 0.836 0.527

2.817 0.851 0.869 0.147

3.635 2.460 0.783 0.447

5.163 4.308 6.591 6.859

8.629 9.472

1.657

3.460

3.501

4.021

3.489 1.00 1.922

3.300 0.868 1.359

n1 ( φ )

0.846 0.957 0.979 0.883

Error (%) R3 ( Ω *cm 2 ) Error (%)

0.371

0.296

1.706 1084 13.07

2.018

1.741

- - - -

- - - -

- - - -

- - - -

- - - -

- - - -

- - - -

- - - -

735

459.65 764

334.90 615.5

22.05

15.58

15.45

13.33

Q2 ( μΤ ) Error (%) W1 (k σ) Error (%)

8.101 15.91 10.85

13.34 9.190

6.751

9.386

13.12

8.216

17.37

25.12 2.618

7.807 3.740

11.64 5.225

7.658 4.239

4.368 10.86

5.148 1.873

5.062 4.669

1.216 2.010 1.056 1.864

1.801 4.073

4.351

3.749

4.449

4.628

4.743

3.590

n2 ( φ )

- -

- -

- -

- -

- -

- -

- -

- -

0.734 0.766 0.719

0.793 0.727

Error (%) Total Error (%)

1.046 4.169

1.200 5.900

2.174 5.615

1.357 4.876

2.635 5.660

1.400

1.821

2.102

1.787

3.689

0.779

2.141

1.575

1000 1100 1200

2198-T3 2198-T8

300 400 500 600 700 800 900 Resistance R 3 [ Ω * cm 2 ]

10 15 20 25 30 35 40 45 50

Immersion time [Hours]

Fig. 4. Variation of the charge transfer resistance of the double layer R 3 as a function of immersion time to 3.5% wt . NaCl solution for AA2198 T3 and AA2198-T8. 4. Conclusions In the present work the corrosion resistances of AA2198-T3 and AA2198-T8 alloys were investigated, and a comparison was performed. The experimental results showed that the microstructure and the mechanisms of corrosion are strongly affected by the thermomechanical treatments on AA2198. The alloy in T3 condition was found to be more corrosion resistant, especially in the first stages of corrosion attack where the dominant corrosion mechanism is the pitting on the surface oxide film, by means of higher values of the oxide film resistance R 2 . The higher kinetics of surface attack in the case of T8 temper, which are related to the higher amount of T 1 precipitates, make this alloy more susceptible to corrosion attack. However, lower decrease rate of the oxide film resistance was noticed in T8 temper when compared against T3 temper. Regarding the charge transfer resistance R 3 , the T8 temper exhibited higher values than T3 after 24 h immersion time as well as lower decrease rate. Thus, it can be concluded that the T8 temper is more susceptible to corrosion attack due to the presence of T 1 precipitates, but superior to T3 concerning corrosion resistance degradation rate.