Microstructure evolution and metallurgical characteristic of bead-on-plate TIG welding of Ti-6Al-4V alloy

The bead geometry of autogenous bead-on-plate tungsten inert gas (TIG) welding performed on Ti-6Al-4V alloy inside an argon inert box chamber was measured for different processing conditions. The microstructural evolution of the weldment was evaluated through optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) technique. The development of residual stress and the texture in the weldment were assessed through the XRD techniques. The full penetration melting for bead-on-plate welding was obtained for high current and low scan speed combination that induces maximum heat input within the experimental domain. Owing to intense heat of the TIG arc, a complex microstructural evolution occurred in the Ti-6Al-4V alloy, which causes transformation of initial beta phase to martensitic alpha' phases. The transformation of initial alpha + beta phase to martensitic alpha' phase enhances the hardness value of the melt pool upto 365 HV0.2, and further at heat affected zone (upto 385 HV0.2) owing to grain refinement. The residual stress developed in the weld melt pool was recorded tensile type, and for increasing the welding current, due to the enhancement of induced heat, the residual stress increased from 140 to 200 MPa (for 80 A) to 240-270 MPa (for 100 A).