The Effect of Laser Beam Welding on Microstructure and Mechanical Properties of Commercially Pure Titanium

Commercially pure titanium sheet with 1.6mm thickness is welded using a continuous wave (CW) 2kW Nd:YAG laser system. The effects of laser process parameters, laser power (LP), welding speed (WS), and hence heat input (HI) on microstructures, tensile, bending and hardness properties are investigated. The results indicate that laser beam welding is suitable for commercially pure titanium, full penetration and the welding seam without defects can be obtained. Vickers microhardness was measured across traverses through the welded sections and along the weld centerline from the top surface. The results suggest that the increase in hardness is directly proportional to the dissolution of small amounts of oxygen, nitrogen, and carbon concentrations along the weld centreline. The maximum hardness achieved in the fusion or weld zone is 258HV, whereas the base material exhibits maximum hardness of 154HV. It has been established that there is tendency of increase in hardness with decrease in lower weld heat input. The tensile, ductility, bending and hardness properties of the joints are corresponding to matrix surface. It has been found that a trend of increased tensile strength with the decrease of welding heat input and a trend of increased tensile strength with the increase of welding cooling rate. As heat input decreases, there will be faster the cooling rate. Considering the effect of heat input on ductility, it was found that the lower the heat input, faster the cooling rate, therefore the larger is the relative elongation and hence the higher the weld's ductility.