Heterogeneous microstructure improves the strength and ductility of a flash-butt welded IN718 alloy joint

Higher strength and ductility are obtained in a flash-butt welded IN718 alloy joint due to an improved heterogeneous microstructure distribution by adjusting the upsetting deformation. With the increase in upsetting deformation, the microstructure distribution of the characteristic zones is effectively adjusted which contains a complete recrystallization zone (RxZ), a thermo-mechanical affected zone (TMAZ) and a coarse grain zone (CGZ). Finer grains and more residual stress are obtained in the heat affected zone (HAZ), which increases the strength and hardness. The improvement of the strength in the HAZ delays the concentration rate of local strain at the weld seam (WS) and enhances the coordination between the HAZ and the matrix. Therefore, the additional ductility is obtained by the coordination between the HAZ and the matrix, which results in a welded sample of UD0.86 achieving the same high strength and ductility as that of the base material.