Effect of keyhole on plasticity-evolved behaviors of thick Ti-6Al-4V laser-arc hybrid welded joint

Revealing plasticity-evolved behaviors of laser-arc hybrid welding welds is indispensable for controlling highreliability Ti-6Al-4V welded joints used in marine equipment. The relationship between dual heat source coupling and the plasticity of welded joints in thick plate titanium alloy is analyzed in this research. The plasticity-enhancing mechanisms based on the action of the keyhole are also elucidated. The results underscore that due to the faster cooling rate, the keyhole effect weakens the texture strengths of the beta and alpha ' phases by 65.8% and 70.3%, respectively, and improves the ductility of the keyhole-affected region by 20% compared to the keyhole-free region. Furthermore, the keyhole region facilitates the generation of small-sized brittle phase alpha ', an increase in the number of small-angle grain boundaries, and easily activated pyramidal-slip systems {10 1 1}< 112 0>, implying improved grain deformability and plasticity. These results have provided valuable insights into the plasticity-enhancing behaviors of thick Ti-6Al-4V laser-arc hybrid welded joints, offering guidance for subsequently regulating the performance of welded joints to achieve superior plasticity welded joints.