Research On Microstructures And Properties Of Laser Welding Joints Of TC4 Titanium Alloy

With the advantages of low density, high strength-to-weight ratio and superior corrosion resistance, titanium alloys have been widely applied in the fields of aircraft and automobile industries. As the laser welding of titanium have some characteristics such as strong energy concentration, good appearance and high efficiency, it becomes a main method for titanium welding. In the practical application of titanium products, the structure constituent and properties of welding joints should satisfy the requirements. So the research of the microstructures and properties of titanium laser welding joints will benefit for the application of titanium laser welding.A slab CO₂ laser beam welding of TC4 alloy with a thickness of 2mm was adopted to investigate the formation of weld, the weld microstructure and the mechanical properties of its joints. It was found that the tensile strength of welding joints was determined by the formation and the microstructure of welding joints. Also it was observed that the tensile strength of the welding joints was decreasing with the increasing of the acutance of undercut. The results indicated that the orientational acicular martensites could increase the tensile strengths of the welding joints, while the coarse columnar grains could reduce the plasticity of joints.The effects of various contents of nitrogen or oxygen in welding joints on the weld surface, the weld microstructure, the weld micro-hardness and the mechanical properties of joints were investigate. It was found that the increase of nitrogen or oxygen contents in joints could worsen protection effect and increase the micro-hardness. The results indicated that the acicular martensites became coarser, the weld strength raised, the plasticity of joints decreased and the fracture morphology became quasi-cleavage fracture from ductile dimple structure with the content of nitrogen or oxygen increased in shielding gas. When the nitrogen or oxygen content in the shield gas individually was 0.5%, the plasticity of joints was not affect.