Effect of laser shock peening on microstructure and fatigue properties of thin-wall welded Ti-6A1-4V alloy

Abstract

Thin-wall welded Ti-6A1-4V alloys are widely used in aero-engines but their fatigue properties are often worsen by thermal influence during the welding process. In this paper, laser shock peening (LSP) was carried out to improve their high cycle fatigue performance. The 3 mm thin-wall Ti-6A1-4V alloy plate was prepared using the tungsten inert gas (TIG) welding first and strengthened by the laser shock peening. The residual stress was measured by X-ray diffraction and results showed that LSP could transfer tensile residual stress into compressive residual stress in the heat-affected zone. In addition, significant grain refinement was observed by electron backscatter diffraction. Moreover, high cycle fatigue test was carried out using step-loading method and results showed the fatigue strength was enhanced by 19.82%. Lastly, the change of fatigue crack initiation (FCI) from surface to subsurface was observed by scanning electron microscope. • Laser shock peening was successfully used to strengthen thin-wall welded Ti-6A1-4V alloy and enhance its fatigue strength. • Welding process introduces tensile residual stress and causes fatigue weak areas in heat-affected zone. • Grain refinement was observed and tensile residual stress changed into compressive residual stress after LSP treatment.