Crevice Corrosion Behaviors Between CFRP and Stainless Steel 316L for Automotive Applications

doi:10.1007/s40195-019-00909-z

Abstract

Abstract:

Carbon fiber reinforced plastics (CFRP) are promising lightweight materials for vehicle applications. 316L is one of the most widely used types of austenite stainless steels and applied in lots of automotive applications. The existence of crevices will result in galvanic corrosion and crevice corrosion when CFRPs and 316L are directly connected. A crevice former for the galvanic system was therefore designed and applied to evaluate the crevice corrosion behaviors and study the mechanism of galvanic crevice corrosion through several electrochemical techniques in this research. The results showed that the crevice corrosion of galvanic systems grew from crevice mouth to the inside crevice and could be divided into four steps, metastable pitting corrosion at the crevice mouth, initiating step of crevice corrosion, propagating step and ending step of crevice corrosion. Because of the influences of the galvanic system, electrode reaction rates were speeded up and the passivation region was shortened at the initiating stage of crevice corrosion. Corrosion rate was observed to be higher in the galvanic system than that in normal crevice systems.

Key words: Crevice corrosion, Galvanic system, Carbon fiber reinforced plastics, 316L stainless steels

Xia-Yu Wu, Jia-Kun Sun, Jia-Ming Wang, Yi-Ming Jiang, Jin Li. Crevice Corrosion Behaviors Between CFRP and Stainless Steel 316L for Automotive Applications[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(10): 1219-1226.

Figures/Tables 14

Table 1 Composition of 316L stainless steel (wt.%)

	C	Si	Mn	P	S	Ni	Cr	Mo	Cu	N
316L	0.021	0.46	1.37	0.034	0.001	10.21	16.39	2.03	0.16	0.034

Table 2 Composition of epoxy carbon non-crimp fabric (wt.%)

Composite	Concentrate	Base material
Epoxy carbon non-crimp fabric (LE)	65	Epoxy resin

Fig. 1 Schematic illustration of specimen assembly for crevice corrosion tests

Fig. 2 Polarization curve of the galvanic system in 1 M NaCl solution at 30 °C

Fig. 3 SEM Morphology of crevice corrosion for the galvanic system after potentiodynamic experiments in 1 M NaCl solution at 30 °C

Fig. 4 Cyclic potentiodynamic result of the galvanic system in 1 M NaCl solution at 30 °C

Fig. 5 SEM Morphologies of crevice corrosion in the galvanic system after cyclic potentiodynamic experiments in 1 M NaCl solution at 30 °C: a the whole crevice area, b metastable pitting besides the crevice edge

Fig. 6 Potentiodynamic-galvanostatic-potentiodynamic curve of the galvanic system in 1 M NaCl solution at 30 °C

Fig. 7 SEM morphologies of crevice corrosion for galvanic system after potentiodynamic-galvanostatic-potentiodynamic experiments in 1 M NaCl solution at 30 °C: a the whole crevice area, b metastable pitting inside the crevice

Fig. 8 Measured potential, current as the function of time in potentiodynamic-galvanostatic-potentiostatic test in 1 M NaCl solution at 30 °C

Fig. 9 SEM morphologies of crevice corrosion for galvanic system after potentiodynamic-galvanostatic-potentiostatic experiments in 1 M NaCl solution at 30 °C: a the whole corrosion, b Zone-I, c Zone-II, d Zone-III, e Zone-IV

Table 3 Repassivation potentials and corrosion depth obtained from the three electrochemical techniques

	Repassivation potential (V)	Max corrosion depth (μm)	Average corrosion depth (μm)
CPP	- 0.256 ± 0.012	2.32	1.67 ± 0.60
PGPD	- 0.122 ± 0.021	84.15	64.77 ± 9.83
PGPS	- 0.100 ± 0.010	97.79	69.71 ± 12.28

Fig. 10 Schematic diagram of crevice corrosion generating process in 316L-CFRP galvanic system

Fig. 11 Polarization of SS 316L with crevice former in galvanic, non-galvanic system

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