Influence of Laser Power and Traverse Speed on Weld Characteristics of Laser Beam Welded Ti-6Al-4V Sheet

In this paper laser beam welding was used for joining 3 mm Ti-6Al-4V alloy sheets in a full penetration butt-weld configuration. Laser beam power and traverse speed were the only parameters varied in an attempt to characterize the influence on weld integrity with specific reference to residual stress and microstructural modifications. The iXRD residual stress data showed a definite influence of traverse speed on residual stresses, with low traverse speeds resulting in an increased tensile residual stresses in the longitudinal direction of the weld whilst in the transverse direction residual stress revealed a more compressive stress state. The residual stress data for this experiment compared favourably with published residual stress data done by synchrotron X-ray diffraction. Weld joint integrity was further analyzed by evaluating the microstructure transformation in the weld nugget. These results revealed a degree of grain growth and the presences of fine acicular beta (needle-like alpha) in prior beta grain boundaries with increased traverse speed. Grain growth was predominantly influenced by the cooling rate which is associated with traverse speed. Additionally, the alpha-phase and beta-phase were characterized in the various weld zones by electron backscatter diffraction (EBSD).