Tensile behavior of a bi-layered bronze/steel sheet: Synergetic effects of microstructure and residual stress

Bi-layered Cu-Pb-Sn bronze/steel sheets serving as raw material for load-bearing shells require urgent upgrading of mechanical properties for service safety. This study investigated the mechanical properties and deformation behaviors of a bi-layered Cu-Pb-Sn bronze/steel sheet prepared by solid–liquid continuous casting (SLC). The samples were identified by two types of bronze microstructures: homogeneous and segregated Pb phase distributions, denoted as HP and SP, respectively. The Pb phase in HP is mainly in the form of uniformly distributed small particles, while in SP, the segregation and high content of large continuous phases are formed at grain boundaries. These samples were tested for their tensile properties and residual stress. We found that the yield strength and fracture elongation of SP are higher than those of HP, contrary to the general understanding that Pb phase segregation will degrade the mechanical properties of Cu-Pb-Sn alloys. Characterization of the fractures and residual stress results suggest that the increase in SP yield strength is attributed to the higher required shear stress for yielding induced by the residual stress state. The higher fracture elongation originates from the formation of multiple cracks that accommodate the bi-layered structure's deformation incompatibility.