Fig. 1 Specimen design drawing

Fig. 2 Salt spray test equipment connection diagram

Fig. 3 Cross-sectional of SEM image and corrosion rate of specimens corroded for 48 h in salt spray under different currents: a 0 A, b 25 A, c 50 A, d 75 A, e 100 A, f 125 A, g 0 A-, h 50 A-, i corrosion rate

Fig. 4 Surface scanning analysis results of positive and negative poles under 50 A current: a, b positive pole, c, d negative pole

Fig. 5 EDS analysis results of positive and negative specimens under 50 A current: a positive pole, b negative pole

Fig. 6 X-ray powder diffraction patterns of positive and negative poles under 50 A current

Fig. 7 XPS spectra of the corrosion product powder composition under 50 A current: a survey spectrum, b O1s spectrum of the positive pole corrosion product, c O1s spectrum of the negative pole corrosion product

Fig. 8 Electrochemical analysis results of the positive and negative poles under 50 A current in 3.5 wt% NaCl solution: a polarisation curve plots, b Nyquist plots, c Bode-phase angle versus frequency plots and d equivalent circuit of EIS

Fig. 9 Corrosion mechanism schematic diagram

Fig. 10 Schematic diagram of directional migration of ions is in liquid film under DC current

Fig. 11 Salt film morphology, composition and formation temperature of the surface of specimen under 125 A current: a morphology of salt film on section, b morphology of salt film on the surface, c XRD analysis results of salt film components and d trend of specimen temperature with the current

Fig. 12 Change of salt film thickness with time under 125 A current lapse