Effects of laser shock peening on microstructure and mechanical properties of TIG welded alloy 600 joints

Laser shock peening (LSP) is a competitive surface strengthening technology for post-weld treatment. In this work, tungsten inert gas (TIG) welded joints of Alloy 600 were treated by LSP to enhance the mechanical properties. The results showed that the tensile residual stress in weld surface was transformed into the compressive stress state after LSP. LSP treatment caused a significant improvement in microhardness and dislocation density in the weld surface. The tensile strength and yield strength of joints after peening on the full gauge part of tensile samples were increased by 10% and 75%, respectively. However, the fatigue life could be improved much more by only peening on the fusion zone and heat affected zone than that of samples peened on the full gauge part. The peening region played a crucial role on the difference of tensile and fatigue properties due to the residual stress distribution, dislocation strengthening and work hardening induced by LSP.