Abstract
Dissimilar butt joints between 1.0 mm thick commercially pure copper and DP800 dual-phase steel sheets were produced by electron beam welding at an accelerating voltage of 60 kV. Beam current and welding speed were varied between 4–20 mA and 6–16 mm/s, respectively, corresponding to a maximum nominal beam power of 1.20 kW. The effects of the beam-current and welding-speed combinations on weld integrity, tensile strength, microhardness, and microstructural heterogeneity were evaluated. Visual and macrographic inspection showed that sound joints were obtained only for selected parameter combinations and that nominal line energy alone did not uniquely determine weld quality. Among the mechanically tested joints, the highest mean ultimate tensile strength was 242.8 ± 3.5 MPa for 8 mA and 6 mm/s, corresponding to 80.9% of the copper base-material strength. Fracture occurred macroscopically on the copper side adjacent to the fusion boundary. A maximum hardness of 452.4 HV0.05 was measured in the fusion zone. SEM/EDS observations revealed Cu-rich and Fe-rich compositional heterogeneity, although the constituent phases were not identified. The results provide insight into the processing window for electron beam butt welding of 1 mm Cu–DP800 sheets and suggest that copper-side softening and local geometric thinning may contribute jointly to failure.