Microstructure and mechanical properties of NAB/steel composite structures by additive manufacturing with BC-MIG wire arc

Nickel-aluminum bronze (NAB) and grade 25 steel composite structures were fabricated using bypass current metal inert gas（BC-MIG）welding arc additive manufacturing technology under water-cooled conditions to evaluate the feasibility of dissimilar metal additive manufacturing. The results showed that under low heat input of BC-MIG welding and high water cooling rate, the surface of the additive manufacturing structure was well-formed with minimal deformation and no defects or cracks were found in the joints. The influence of heat treatment on the microstructure and mechanical properties was studied. Heat treatment promoted the mutual diffusion of Cu and Fe elements, and the diffusion layer increased from 4 μm to 17 μm, and no Fe-Al intermetallic compound layer was formed at the interface. Residual stresses near the interface were studied by X-ray diffractometer. The results showed that under water-cooling conditions, the residual stresses of steel were distributed among −350 MPa to −250 MPa, while the residual stresses of NAB varied significantly from −550 MPa to 90 MPa. Tensile test results showed that after heat treatment, the tensile strength of the structure decreased slightly due to the reduction of residual stress, but the elongation was significantly improved.