Mechanical Properties and Fracture Behavior of an EBW T2 Copper–45 Steel Joint

The dissimilar joining of T2 copper to 45 steel was performed by electron beam welding (EBW). Full-strength joints were obtained, and the highest tensile strength was found to be 270 MPa, which is almost equal to the strength of copper. Moreover, the macroscopic morphology of the tensile fracture exhibited an obvious necking phenomenon and features such as dimples, and spherical structures were found via scanning electron microscopy (SEM). These results indicated that the fracture of the T2 copper–45 steel joint is a mixed mode of cleavage and ductile fracture. Meanwhile, the fracture toughness was determined using the small punch test (SPT) with a drop rate of 0.5 mm/min. SEM imaging of the fracture surfaces revealed that the fracture was controlled by microscopic void nucleation and always occurred in the copper-side heat affected zone (HAZ). Finally, mutual verification between the numerical simulation of the finite element and the SPT results confirmed that the fracture first occurred in the copper-side HAZ due to the toughness difference.