Effects of Laser Shock Processing on Mechanical Properties of Laser Welded ANSI 304 Stainless Steel Joint

With the rapid development of engineering component with integration, high-speed and multi-parameter, traditional techniques haven't met practical needs in extreme service environment. Laser welding, a new welding technology, has been widely used. However, it would generate the drop of mechanical properties for laser welded joint due to its thermal effect. Laser shock processing (LSP) is one of the most effective methods to improve the mechanical properties of laser welded ANSI 304 stainless steel joint. In this paper, the effects of LSP on the mechanical properties of laser welded ANSI 304 stainless steel joint have been investigated. The welded joint on the front of the tensile samples is treated by LSP impacts, and the overlapping rate of the laser spot is 50%. The tensile test of the laser welded joint with and without LSP impacts is carried out, and the fracture morphology of the tensile samples is analyzed by scanning electron microscope (SEM). Compared with the yield strength of 11.70 kN, the tensile strength of 37.66 kN, the yield-to-tensile strength ratio of 0.310 7, the elongation of 25.20%, the area reduction of 32.68% and the elastic modulus of 13 063.876 MPa, the corresponding values after LSP impacts are 14.25 kN, 38.74 kN, 0.367 8, 26.58%, 42.29% and 14 754.394 MPa, respectively. Through LSP impacts, the increasing ratio of the yield strength and tensile strength are 121.79% and 102.87%, respectively; the elongation and area reduction are improved by 5.48% and 29.38%, respectively. By comparing with coarse fracture surface of the welded joint, the delamination splitting with some cracks in the sharp corner of the welded joint and asymmetric dimples, LSP can cause brighter fracture surface, and finer and more uniform dimples. Finally, the schematic illustration of dimple formation with LSP is clearly described. The proposed research ensures that the LSP technology can clearly improve the yield strength, tensile strength, yield-to-tensile strength ratio, elongation, area reduction and elastic modulus of the welded joint. The enhancement mechanism of LSP on laser welded ANSI 304 stainless steel joint is mainly due to the fact that the refined and uniform dimples effectively delay the fracture of laser welded joints.