Abstract: Strength and ductility are typically mutually exclusive in traditional copper-steel joints. This work proposes a strategy to overcome the inherent trade-off between strength and ductility through high speed electron beam welding with a preferred deflection to facilitate the in-situ formation of Fe-rich particles in the Cu matrix. The Fe-rich particles with an average diameter of 178.5 nm feature a 3D spatial network distribution across practically the entire joint. The obtained joint reinforced with such Fe-rich particles achieves ultimate high tensile strength (413 MPa) while maintaining excellent ductility (22%). The improved strength of the copper-steel joint is derived from the combined effects of dislocation strengthening and grain refinement strengthening, while the increase in room-temperature ductility is mainly due to the high Schmid factor up to 0.454, which promotes the primary slip system to initiate easily during tensile deformation. This work provides a novel perspective on creating copper-steel joints in terms of achieving microstructural refinement and outstanding strength-ductility synergy.

Key words: Copper-steel joints, In-situ Fe-rich particles, 3D spatial network-microstructure, Electron beam welding