Gradient-grained layered Cu-Ni-Si-Cr alloy fabricated by explosive welding: microstructure and mechanical properties

To overcome the long-standing trade-off between strength and ductility in copper alloys, this study proposes the construction of a gradient-grained layered heterostructure using explosive welding. Three plates of a Cu-Ni-Si-Cr alloy with distinct grain sizes—fine, medium, and coarse—were prepared by solution treatment and subsequently bonded into a three-layer composite plate through two successive explosive welding processes. The microstructure, mechanical properties, and deformation behavior of the composite were systematically characterized using optical microscopy, scanning electron microscopy, electron backscatter diffraction, and digital image correlation. The results show that the bonding interfaces exhibit a typical wavy morphology, accompanied by localized melted zones and adiabatic shear bands. The composite achieves a yield strength of 402.5 MPa, which exceeds the value of 304.0 MPa predicted by the rule of mixtures, while maintaining an elongation to fracture of 16.8%. Quantitative strengthening analysis reveals that dislocation strengthening contributes the most to the yield strength, primarily due to the high-density dislocations introduced by the intense impact and deformation during explosive welding. Fracture analysis indicates significant interlayer deformation incompatibility, with crack initiation occurring at interface 2. Shear bands and thickness reduction are observed in the fine- and medium-grained layers, but not in the coarse-grained layer. Digital image correlation confirms the presence of a pronounced strain gradient and strain localization along the thickness direction during tensile loading, which ultimately drives crack initiation and propagation at interface 2. This study elucidates the critical role of hetero-interfaces in governing interlayer deformation partitioning and failure in gradient-grained heterogeneous Cu-Ni-Si-Cr alloy composites, and provides a viable approach for fabricating high-performance layered gradient heterogeneous copper alloys via explosive welding.