Role of layer structure in enhancing ductility of bi-layered bronze/steel sheet revealed by in situ study

Improving the strength–ductility combination is a critical challenge in metallic materials. Cu–Pb bronze alloys, commonly used in bearing materials, require superior mechanical properties and service safety. However, they face a significant reduction in ductility due to concentrated plastic deformation within the low-strength Pb phase. To address this issue, the solid–liquid continuous casting (SLC) method was used to overlay Cu–Pb alloy onto a mild steel substrate, forming a bi-layered structure that significantly enhances overall ductility. An in situ tensile test in conjunction with digital image correlation (DIC) and electron back-scattered diffraction (EBSD) methods revealed that localized strain within the bronze layer concentrates at Pb phases and transitions into dispersive strain bands. This transformation is attributed to the constraint from the layered structure. The well-bonded interface, demonstrated by the interface-affected zone (IAZ), ensures coordinated deformation of the bi-layered sheet. Moreover, the layered structure effectively constrains individual crack propagation and encourages a multiple-crack behavior.