方形光斑激光冲击强化金属表面的耐腐蚀性能及机理

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

使用25J和30J脉冲能量的方形光斑激光冲击强化技术对20CrMnTi钢表面进行强化。测量强化后样品表面的分层设色形貌图、粗糙度、显微硬度和残余应力,研究样品的极化曲线和盐雾腐蚀后的表面形貌。结果表明:激光冲击强化使得表层材料发生塑性变形,试样表面粗糙度Ra降低到0.433μm,显微硬度得到提高,并产生较大的残余压应力。合适的激光功率密度使得材料的强化层和钝化膜的密度增加,产生的横向残余压应力使得钝化膜更加稳定,从而提高材料的耐腐蚀性能。过大的激光功率密度导致材料表面出现压痕、铝箔发生烧蚀等现象,使得Cl-在压痕缺陷处聚集,材料表面局部产生拉应力,表面钝化膜被破坏,加快表面的腐蚀速率。

The surface of 20 CrMnTi steel was strengthened by the square-spot laser shock peening（LSP）with 25 Jand 30 Jpulse 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 Raof the specimens reduces to0.433μm,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.