## 3 Experimental Results and Analysis
### Corrosion Behavior Analysis  
Figure 5 delineates the correlation between corrosion potential (Ecorr) and corrosion current density (Icorr) across varying laser energy densities and spot overlap rates. Ecorr serves as an indicator of a material's susceptibility to corrosion under electrochemical conditions, while Icorr quantifies the rate of corrosion. Typically, materials exhibiting Icorr values are considered to possess superior corrosion resistance. Concurrently, Figure 6 compares the corrosion potential and current of the material post-laser cleaning against the laser-cleaning parameters, revealing an Ecorr of 752 mV on the rusted 20-gauge steel sample's surface and an Ecorr of 541 mV on the unrusted sample. The reduction in Icorr following laser cleaning signifies an enhancement in the corrosion resistance of the material's surface. Remarkably, the sample treated with a laser energy density of 4.26 J/cm\({}^{2}\) and a 75% spot overlap exhibited the lowest Icorr among all samples, indicating a notable improvement in corrosion resistance relative to the original 20-gauge steel. Conversely, increasing the laser energy density to 5.68 J/cm\({}^{2}\) diminished the corrosion resistance, suggesting that excessive laser energy can inflict damage on the substrate.  
Figure 4: At 75% spot overlap: (**a**) microhardness indentation and test point position; (**b**) change in microhardness values before and after laser cleaning.  
Figure 7 shows the electrochemical impedance spectrum (EIS) of 20 steel. Generally, the diameter of the Nyquist plot curve is indicative of the charge transfer resistance with a larger diameter suggesting enhanced corrosion resistance. Notably, the impedance diameters of the sample surfaces after laser cleaning exceeded those of the unpolarized surfaces, demonstrating that laser cleaning effectively improves corrosion resistance. The maximum  
Figure 5: Tafel curves of the rust, bare, and laser-treated samples with the laser fluence of (a) \(1.42\,\mathrm{J/cm^{2}}\), (b) \(2.28\,\mathrm{J/cm^{2}}\), (c) \(4.26\,\mathrm{J/cm^{2}}\), (d) \(5.68\,\mathrm{J/cm^{2}}\).  
Figure 6: Electrochemical parameters of Tafel curves for rusted, bare 20 steel, and laser-cleaned surfaces with different laser parameters (energy density and overlap rate), (a) Ecorr modulus, (b) Icorr modulus.  
curve diameter, indicating optimal corrosion resistance, was observed at a laser energy density of 4.26 J/cm\({}^{2}\). Furthermore, to provide a more comprehensive understanding of the surface corrosion behavior of trusted 20-gauge steel post-laser cleaning, an equivalent circuit model was employed to fit the EIS data. Figure 8 illustrates this model, where R\({}_{\text{s}}\) represents the solution resistance, CPE\({}_{\text{dl}}\) denotes the double-layer capacitance, and R\({}_{\text{ct}}\) signifies the charge transfer resistance. To enhance the precision of the fitting, a Constant Phase Element (CPE) was utilized in place of traditional capacitance.  
\[ZCPE=[Q(j\omega)n]-1 \tag{3}\]  
where \(Q\) signifies the magnitude of the CPE, \(j\) represents the imaginary unit, \(\omega\) stands for the angular frequency, and n denotes the exponent of the CPE index. The specific fitted values are presented in Table 2, where it is worth noting that a bigger charge transfer resistance R\({}_{\text{ct}}\) generally indicates superior corrosion resistance. Upon analyzing the data presented in Table 2, it becomes evident that the corrosion resistance of the laser-cleaned surfaces exhibits a significant improvement when compared to the initial untreated surfaces. Notably, the highest level of corrosion resistance is achieved at an energy density of 4.26 J/cm\({}^{2}\). Its R\({}_{\text{ct}}\) is 1.218 times that of the original 20 steel.  
Figure 7: Rusted EIS, bare 20 steel substrate, laser-cleaned surface in different melts: (**a**) Nyquist plot, (**b**) the Bode plot, (**c**) Bode phase angle plot, (**d**) equivalent circuit of the EIS curves.