Figure 1 shows the equivalent circuit diagram of three parts of lzqt600-3 ductile iron profile in 3.5% NaCl solution. R1 is the solution resistance of the electrolytic cell, R2 is the polarization resistance of the electrode charge transfer. The corrosion resistance of the sample depends on the R2 value. CPE is a constant phase angle element.
Figure 2 shows the EIS of three parts of lzqt600-3 ductile iron profile in 3.5% NaCl solution. Using z-view software and combining with the equivalent circuit diagram in Figure 3-11, the electrochemical impedance spectra of three parts of lzqt600-3 ductile iron profile were fitted, and the fitting values of each circuit element were obtained. It can be seen from the figure that there is a semicircle capacitive reactance arc in the middle and high frequency region. The higher the diameter of the half ring, the better the corrosion resistance. In Fig. 2, the capacitive reactance arcs of three samples at different positions start from the same starting point, so the capacitive reactance arc diameters of the three samples can be directly compared. By comparison, it can be concluded that the capacitive reactance arc diameters at the edge and 1 / 2R are close to and larger than those at the center.
The solution resistance R1 of the three parts is small, and the polarization resistance R2 of electrode charge transfer is 1375, 1394 and 859.4 Ω· cm-2 from the edge to the center, which represents the ability of the material to resist corrosion, that is, the larger the R2 value, the more resistant the material can be to corrosion. The results of capacitive impedance arc diameter in Fig. 2 are consistent. The capacitance of the passive film on the sample surface is expressed by cpe-t. for the results of cpe-t fitting, the smaller the value is, the thicker the passivation layer covering the surface of the sample is or only a few defects are produced, the better the corrosion protection can be achieved. The cpe-t values from the edge to the heart were 1.4 × 10-8, 1.3 × 10-8 and 2.6 × 10-8 f · cm-2, respectively. Therefore, it can be inferred that the corrosion resistance tendency of different parts is: 1 / 2R > edge > center. This is due to the randomness of sampling in the profile, and the liquid core at the lower 1 / 2R is higher than that at the lower 1 / 2R. Therefore, this part is similar to the edge, also has a higher nucleation rate, and the corrosion resistance is not significantly different from the edge.