Fine microstructure characterization of titanium alloy laser narrow gap welded joint

In this paper, the microstructure of narrow gap laser welded joint of 45 mm Ti6321 titanium alloy was characterized. The microstructure characteristics of Laser self-fusion and laser-multi-pass-narrow-gapfilling layer were observed by metallographic microscope, and the phase morphology was analyzed by transmission electron microscope. The results show that the joint was obtained using the laser-multipass-narrow-gap welding, and no volumetric defect is observed. The weld grain of self fusion welded bead tends to be equiaxed with lots of needle α’, and the width of weld metal needle α’ was 0.4 μm. The heat affected zone is columnar crystal with lamellar α, and The width of heat affected zonelamellarα was 2–4 μm with a large number of dislocation tangles. The weld grains of laser-multi-pass-narrow-gap filler bead are coarse columnar grains with staggered acicular α’, and the width of acicular α’ in weld metal is less than 1 μm with number of dislocations. The heat affected zone is thick lamellar microstructure with a width of 2–4 μm with a large number of dislocation entanglement and packing. The microstructure evolution law is related with heating temperature and cooling rate.