Influences of laser welding on fatigue propertis of SPF/DB Ti-6Al-4V alloy

Tensile and fatigue properties of SPF/DB titanium alloy and its laser welded joints were investigated experimentally, and S-N curve was obtained.Microstructure and fatigue fracture features were observed, and influences of laser welding on fatigue properties of SPF/DB Ti-6Al-4V alloy were analyzed.It showed that tensile strength of the laser welded joints of SPF/DB Ti-6Al-4V alloy is less than that of the base metal slightly, but fatigue strength of the laser welded joints, about 40% of its tensile strength, is less than that of the base metal obviously.SPF/DB Ti-6Al-4V alloy is composed of equiaxed structure with αand β phases, and its laser welded joints are composed of weave structure with α, acicular martensiteα' and β phases.Uniformal and coarse microstructure is an important factor causing decrease of fatigue properties of laser welded joints.The fracture of SPF/DB Ti-6Al-4V alloy is plastic failure, but the welded joints are quasi-cleavage fracture which decreases fatigue properties obviously.At the same time the minute flaws below the surface of weld are usually the origin of fatigue failure of laser welded joints.