Probing joining mechanism of Ti6Al4V-SS316L steel rods in pressure-controlled joule-heat forge welding

Ti6Al4V-SS316L steel joints are vital in automotive and nuclear industries due to lightweight, creep, and corrosive resistivity; however, their fusion-based weldments readily form brittle phases under uncontrolled meltsolidification dynamics. Plasticity-induced solid-state welds are recourses, but uneven softening and metal upset remain intricate and cause failure. Pressure-controlled joule-heat forge welding offers plastic deformation with the maneuvered pressure, current and forging strokes. Experimental studies reveal local homogeneous plastic flow of dissimilar metal interfaces for a high-strength metallurgical bond at low temperatures using this process. However, the underlying weld mechanics remains to be uncovered. Thus, to address this shortcoming, finite-element-based calculations of concurrent electric resistive heating and pressure-displacement-induced plastic flow of dissimilar interfaces are modeled by a coupled electric, thermal and dynamic stress analysis. The estimated transient thermal histories and different weld geometries provide insight into the joining procedure and are later validated to the measured results. The mechanics of locally controlled plastic deformation are illustrated with evolved stress-strain transients that reasonably indicate differential responses of dissimilar cross-sections to the applied forging, except at the interface that forms metallic joints. Further, the computed results show a homogeneous temperature increment rate at the center and periphery of the deformed crosssections. The microscopically observed weld structures indicate dynamic recrystallization and smooth hardness transit across bimodal alpha-beta phases with elongated titanium alpha-grains and refined annealed twin austenite in steel.