Numerical and experimental investigation of pressure-controlled joule-heat forge welding of steel tubes

Abstract

Joining metallic tubes without melting is an enroute to impermeable and high-strength joints for lightweight and transport applications. Friction-based joining processes avoid melting and solidification defects, although the generated metallurgical bonding remains critical due to the uncontrolled differential interface heating and plastic deformation. Pressure-controlled joule-heat forge welding obtains a joint in a solid state with uniform plastic deformation of faying interfaces. A short-duration high-current pulse is discharged across the metallic tube assembly under the electrically conducting copper-steel plates. A high-pressure contact and thermal softening allow a radially outward metal plastic flow with the expulsion of oxide films. The joint evolution is further controlled with the pushing rate to a set distance. This study marks the novel effort to examine the thin-walled steel tubes joining with an integrated experimental and numerical approach. The computational analysis based on the finite element approach reveals the time instants of the interfacial contact pressure, thermal softening, and plastic flow behavior for the joint formation. The welded and upset-out region indicates uniform recrystallization of radially aligned grains with a consistent microhardness distribution. The actual welded geometry dimensions matched fairly well with the calculated dimensions.