Enhancing the interface bonding of steel/copper bimetallic structures fabricated via WAAM by suppressing Cu penetration

Steel/copper bimetallic structures fabricated via typical wire arc additive manufacturing (WAAM) exhibit superior comprehensive performance; however, they typically exhibit weak interfaces because Cu penetrates the steel, thereby producing thermal cracks. This study proposes an economical WAAM fabrication process that regulates the heat input through pulsed deposition integrated with a path optimization strategy to enhance steel/copper interface bonding. Compared with the conventional process, the proposed process exhibits the advantages of low heat input, less splashing, and a more optimized heat source distribution, thereby preventing localized overheating and suppressing copper penetration. Computed tomography and optical microscopy revealed a dense microstructure without obvious cracks and voids. Both the steel- and copper-deposited layers exhibited uniform microstructures, with the steel-deposited layers composed primarily of ferrite and pearlite and the copper-deposited layers consisting of columnar crystals. A multi-element diffusion zone (Fe-Cu-Sn) was observed at the bimetallic interface, which produced strong metallurgical bonding. The penetration of Cu into steel was effectively suppressed by precise heat input control using the proposed strategy. The strong interface achieved an ultimate tensile strength of 366 MPa, which falls between that of the steel and copper matrices, with ductile fracture occurring on the copper side, indicating its higher strength compared to the copper side. The strengthening of the steel/copper bimetallic interface is attributed to the formation of a dense metallurgical transition zone and the suppression of Cu penetration into the steel.