Intrinsic relationship between thermal cycle, microstructural heterogeneity and mechanical properties of double-side TIG welded Ti–6Al–4V joint

Double-side welding exhibits the significant advantages for the fabrication of thick alloy plates. Whereas the inhomogeneity of microstructure was generally induced, this inhomogeneity's formation mechanism and its effects on the plastic deformation and mechanical properties lacks in-depth study. In the present study, the intrinsic relationship between the thermal cycle, microstructural heterogeneity and the mechanical properties was clarified through the stratified analysis in the Ti–6Al–4V alloy with a thickness of 10 mm fabricated by the double-side tungsten inert gas (TIG) welding. The joint was formed by two weld seams and the fusion zone (FZ), exhibiting an hourglass shape. The FZ and heat-affected zone (HAZ) were characterized by the basket-weave structure, and the thickness of lamellar α-phase varied in different regions. The Vickers hardness and strength in the FZ gradually decreased across the layer due to the coarsening of lamellar α-phase. The plasticity varied, which was mainly dependent on the formation of equiaxed α-phase and the activation of dislocations. After the post-weld heat treatment (PWHT), the equiaxed α-phase was formed along with the basket-weave structure, resulting in the uniform distribution of mechanical properties.