## 4 The Influence of Surface Residual Stress on Corrosion Resistance
### The Influence of Surface Residual Stress on Corrosion Degradation Performance of the Material  
Figure 14 shows the stress-strain curves of different surface residual stress specimens after 4 h of electrolytic corrosion. It can be seen in Figure 14 that the mechanical properties of different surface residual stress specimens show different degrees of deterioration after 4 h of corrosion; the specimen with a surface residual stress of \(-120.2\) MPa has the most obvious reduction in tensile strength after electrolytic corrosion, which is \(18.88\%\) lower than before electrolytic corrosion. Figure 15 shows the measured tensile strength and elongation curves of different surface residual stress specimens after 4 h of corrosion. It can be seen from Figure 15 that with the increase in surface residual compress stress on the specimen, the tensile strength of the specimen tends to increase after corrosion. In contrast, the elongation tends to decrease gradually. When the surface residual stress is \(-335.84\) MPa, the specimen has a maximum tensile strength of \(548.8\) MPa, and the elongation is \(17.56\%\). In comparison, the specimen with the surface residual stress of \(-120.2\) MPa has a minimum tensile strength of \(494.44\) MPa, and the elongation is \(19.26\%\). With the increase in surface residual compress stress, after corrosion, the tensile strength of the specimen increased by \(10.9\%\), and the elongation decreased by \(9.7\%\). With the increase in surface residual compress stress on the specimen surfaces, the tensile properties of the specimens are relatively good after corrosion. The specimen with a surface residual stress of \(-335.84\) MPa under the experimental  
conditions described in this paper has a better tensile strength after 4 h of corrosion and has the best corrosion resistance. The reasons for the above phenomenon are that when the specimen material is subjected to external force, the maximum surface load changes as the residual stress in the surface layer changes. The larger surface residual compress stress can effectively reduce the oxidation susceptibility of grain boundaries, inhibit the destruction of crystal structure, and reduce the occurrence of stress corrosion and pitting corrosion at grain boundaries. Meanwhile, although the specimens with large surface residual compress stress have large surface roughness after corrosion, shot peening refines the surface material structure of the specimen and inhibits surface cracks during stretching. The reasons mentioned above  
Figure 14: Stress–strain curves of specimens with different surface residual stresses before and after corrosion. (**a**) \(-\)120.2 MPa; (**b**) \(-\)215.47 MPa; (**c**) \(-\)293.27 MPa; (**d**) \(-\)335.64 MPa. Figure 15: Curves of tensile strength and extensibility after electrolytic corrosion with different surface residual stresses. reduce the emergence and extension of specimen material microcracking due to the stress concentration caused by pitting corrosion and the surface topography. In addition, as the residual compress stress inhibits corrosion of the surface material of the specimen, the strength of the specimen with higher residual stress on the surface is less affected by corrosion. Therefore, as the residual compressive stress on the surface layer increases, the tensile strength of the specimen material shows a gradual increase. However, with the increase in surface residual, a certain thickness of a fine crystal layer is formed on the surface of the material, which leads to surface hardening and a certain degree of reduction in the plastic properties of the specimen material. Therefore, elongation tends to decrease with the increase in the residual compress stress on the surface of specimens. Comparing different surface residual stress specimens, the specimen with a surface residual stress of \(-335.64\) MPa has the best corrosion resistance. Meanwhile, to obtain better corrosion resistance, the shot peening intensity could be appropriately increased during the shot peening process.