Resistance upsetting welding of Zr-Sn/Zr-Nb alloy: Material flow behavior, bonding mechanism and performance in extreme environments

In the process of resistance upsetting welding (RUW) of Zr-Sn/Zr-Nb alloy in nuclear fuel rods, the quality of the joint is unstable, the bonding is not strong and the sealing is poor because of the inaccurate control of the parameters such as forging forces and current. The effects of different forging forces on the joint were investigated through microstructure characterization and thermal-electric-mechanical coupling numerical simulation. By revealing the evolution of grain morphology, twin density, material flow, grain boundary proportion, so as to explain the plastic deformation characteristics and microstructure evolution of joints under large current, local high strain and high temperature. The comprehensive properties of the joint are evaluated by water corrosion, bursting test and tensile test. Water corrosion only thickens the oxide layer near the self-healing line, with the thickness of the oxide layer in other areas being similar to that of the base metal. The joints with different forging forces fractured in the area far from the weld regardless of the bursting or tensile tests. The large forging force accelerates the material flow of the joint, resulting in a rapid narrowing and elongation of the weld nugget compared to the low forging force.