Microstructure and mechanical properties of laser welded Ti-6Al-4V (TC4) titanium alloy joints

Abstract

Laser beam welding (LBW) was applied to join 3 mm thick TC4 titanium alloy plates in this study. Three-factor and three-level orthogonal experiments were designed to choose the best welding parameters through the analysis of range and variance. The microstructures of the welded joints were analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The mechanical properties of the welded joints were analyzed by tensile tests. The experimental results indicated that the defocused position had the largest effect, followed by the laser power and welding speed. The optimal welding parameters were laser power 2.3 kW, welding speed 0.04 m/s and defocused position 0 mm. The heat-affected zone (HAZ) consisted of α′ martensite, primary α phase (αp) and primary β phase (βp). In the fusion zone (FZ), the acicular α′ martensite was distributed in the β columnar grains. The tensile strength of the laser welded joint under the optimal welding parameters was 985 MPa, which is less than that of the base metal (BM). The peak value of the grain misorientation angle in the HAZ was related to the amount of martensite. The laser welded joints with finer martensite and equiaxed α + β would have better mechanical properties. The grains in the HAZ had a preferred orientation in the {001} direction.