Study on grain size and microstructure of TC4 titanium alloy TIG and laser welding joint

The TC4 sheet was welded by TIG and laser welding technology. The effects of TIG welding current, welding speed and laser output power on the grain size, microstructure and microhardness of TC4 titanium alloy welded joint were analyzed. The experimental results show that laser welding had a lower heat input, and the width of weld zone and heat-affected zone was significantly reduced under the condition of complete penetration of TC4 titanium alloy sheet. The grain size of TIG welded joint increased with the increase of heat input. The grain size of welded joint decreased gradually with the increase of distance from the center of weld. The laser welded joint showed the characteristics of widmanstatten structure with the finer acicular martensite α' phase. The microstructure of martensite α' near the heat-affected zone was basket shaped, while the microstructure of martensite α' near the base metal was double phase of untransformed α phase and needle shaped martensite α'. With the increase of the distance from the weld centerline, the martensite content decreased gradually, and the weld microhardness decreased. At the same time, compared with TIG welding, TC4 laser welded joint had higher microhardness.