Corrosion Resistance and Mechanism of Metallic Surface Processed by Square-spot Laser Shock Peening

The surface of 20CrMnTi steel was strengthened by the square-spot laser shock peening (LSP) with 25J and 30J pulse energy. The layered style morphology, roughness, micro-hardness and residual compressive stress of the strengthened sample surface by LSP were test. The polarization curve and the corrosion morphology were investigated. The results show that, plastic deformation occurs in the surface after square-spot LSP, the surface roughness R-a of the specimens reduces to 0.433 mu m, and micro-hardness improves, great residual compressive stress is formed. The appropriate laser power density of LSP increases the density of the strengthened layer and passive film on the surface, and the transverse residual compressive stress makes the passive film more stable, and improves the corrosion resistance of materials. But the too large laser power density will cause the generation of pit defects in the material surface and the ablation of Al foil. Thus the Cl- is accumulated at the pit defects, the local tensile stress is generate on the surface of the material, and the surface passive film on the material is destroyed, and degrade the performance of corrosion resistance of the material.