Electrochemical corrosion behavior of 2A02 Al alloy under an accelerated simulation marine atmospheric environment

doi:10.1016/j.jmst.2018.09.060

Abstract

Abstract:

The corrosion behavior of 2A02 Al alloy under simulated marine atmospheric environment has been studied using mass-gain, scanning electron microscope/energy dispersive spectroscopy (SEM/EDS), laser scanning confocal microscopy, X-ray diffraction spectroscopy and localized electrochemical methods. The results demonstrate that the relationship between the corrosion induced mass-gain and the corrosion time is in accordance with the power rule. The mass-gain increases gradually during the corrosion time, while the corrosion rate decreases. With ongoing of the corrosion, corrosion products film changed from a porous to a compact structure. The various spectroscopic data show that the corrosion products films composed mainly of Al(OH)₃, Al₂O₃ and AlCl₃. The electrochemical corrosion behavior of the 2A02 Al alloy was studied by electrochemical impedance spectroscopy (EIS).

Key words: Thin electrolyte layers, Atmospheric corrosion, 2A02 Al alloy, EIS

Min Cao, Li Liu, Zhongfen Yu, Lei Fan, Ying Li, Fuhui Wang. Electrochemical corrosion behavior of 2A02 Al alloy under an accelerated simulation marine atmospheric environment[J]. J. Mater. Sci. Technol., 2019, 35(4): 651-659.

Figures/Tables 14

Fig. 1. Optical micrograph of 2A02 Al alloy.

Fig. 2. Schematic of a self-designed special experimental device to simulate marine atmospheric environment.

Fig. 3. (a) Laminated microelectrode system under 4 ± 0.2 mg/cm2 solid NaCl deposit in (98 ± 2)% humidity at 60 °C, (b) the optical image of the distance between each thin slice.

Fig. 4. Mass gain of 2A02 Al under solid NaCl deposit in (98 ± 2)% relative humidity at temperature of 60 °C with respect to exposure time.

Fig. 5. SEM images of the surface morphologies of 2A02 Al alloy under solid NaCl deposit in (98 ± 2)% relative humidity at 60 °C over different time: (a) 24 h, (b) 72 h, (c) 120 h, (d) 200 h.

Fig. 6. EDS analysis of 2A02 Al alloy under solid NaCl deposit in (98 ± 2)% relative humidity at 60 °C: (a) EDS results of region A in Fig. 5(a), (b) EDS results of region B in Fig. 5(b), (c) EDS results of region C in Fig. 5(c), and (d) EDS results of region D in Fig. 5(d).

Fig. 7. LSCM morphologies of 2A02 Al alloy substrate on removal off corrosion products under solid NaCl deposit in (98 ± 2)% relative humidity at 60 °C in different corrosion time: (a) 24 h, (b) 72 h, (c) 120 h, (d) 200 h, (e) the calculated measured results of corrosion pitting depths. This result was corresponding to Fig. 7(a-d) and got from calculated results by LSCM own software OLS4000.

Fig. 8. Cross-section morphologies of 2A02 Al alloy under solid NaCl deposit in (98 ± 2)% relative humidity at 60 °C in a different time: (a) 24 h, (b) 72 h, (c) 120 h, (d) 200 h.

Fig. 9. Chemical composition of the corrosion products on 2A02 Al alloy under solid NaCl deposit in (98 ± 2)% relative humidity at 60 °C in different corrosion time.

Fig. 10. EIS results of 2A02 Al alloy under solid NaCl deposit in (98 ± 2)% relative humidity at 60 °C in different corrosion time: (a) Bode plots, (b) Nyquist plots.

Fig. 11. Equivalent circuit and its possible corresponding physical structure for the 2A02 Al alloy under a thin layer electrolyte. Rs is the solution resistance, Q1 is the outer layer capacitance including the passive film corrosion products, R1 is the resistance of the corrosion product, Q2 is the double layer capacitance of the anodic site. Rct is the charge transfer resistance.

Table 1 Fitted results of the equivalent circuit in Fig. 11.

Time (h)	R_s (Ω cm²)	Q₁ (10^-6 Ω^-1 cm^-2)	n₁	R₁ (Ω cm²)	Q₂ (10^-6 Ω^-1 cm^-2)	n₂	R_ct (Ω cm²)
24 h	21.04	126.4	0.6878	76.60	43.73	0.3237	7494
48 h	86.72	10.47	0.8	10.03	73.37	0.6746	15950
72 h	149.5	8.155	0.8	250.3	62.11	0.6018	34420
96 h	3106	6.998	0.8	518.5	49.14	0.5392	49060
120 h	16.33	2.659	0.8	605.3	51.59	0.5006	55390
144 h	389.6	7.668	0.4584	582.2	46.97	0.4542	89680
200 h	306.9	3.876	0.4433	660.6	48.85	0.4446	130600

Fig. 12. Variation of the (a) Rct and (b) 1/Rct (corrosion rates) under solid NaCl deposit in (98 ± 2)% relative humidity at 60 °C in different corrosion time.

Fig. 13. 2A02 Al alloy corrosion mechanism under solid NaCl deposit in (98 ± 2)% relative humidity at 60 °C: (a) the early stage, (b) the later stage.

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