Interfacial Characteristics and Formation Mechanisms of Copper–steel Multimaterial Structures Fabricated via Laser Powder Bed Fusion Using Different Building Strategies

Laser powder bed fusion (LPBF) is an innovative method for manufacturing multimaterial components with high geometrical resolution. The LPBF-printing sequences of materials may be diverse in the actual design and application of multimaterial components. In this study, multimaterial copper (CuSn10)–steel (316 L) structures are printed using different building strategies (printing 316 L on CuSn10 and printing CuSn10 on 316 L) via LPBF, and the characteristics of two interfaces (the 316 L/CuSn10 or “L/C” and CuSn10/316 L or “C/L” interfaces) are investigated. Subsequently, the interfacial melting mode and formation mechanisms are discussed. At the L/C interface, the keyhole melting mode induced by the high volumetric energy density (E_L/C = 319.4 J/mm³) results in a large penetration depth in the pre-solidified layer and enhances laser energy absorption, thus promoting the extensive migration of materials and intense intermixing of elements to form a wide diffusion zone (∼400 μm). At the C/L interface, the conduction mode induced by the low volumetric energy density (E_C/L = 74.1 J/mm³) results in a narrow diffusion zone (∼160 μm). The interfacial defects observed are primarily cracks and pores. More cracks appeared at the C/L interface, which is attributable to the weak bonding strength of the narrow diffusion zone. This study provides guidance and reference for the design and manufacturing of multimaterial components via LPBF using different building strategies.