The impact of interfacial characteristics on the interfacial properties of 316 L/CuSn10 multi-material manufactured by laser powder bed fusion

Multi-material additive manufacturing (MMAM) enables the simultaneous creation of multi-material components in a single process, accomplishing customized different performances in specific regions of the same components. In particular, the copper-steel multi-material structure can provide considerable strength and high thermal conductivity, thus playing a crucial role in electronic components, heat exchangers and injection molds. However, few studies have explored the relationship between the microstructure and properties of the copper-steel fusion zone. Therefore, this study aims to reveal the heterogeneous evolution of the microstructure in the copper/steel fusion zone and its impact on the interfacial properties of 316 L/CuSn10 multi-material structure fabricated by laser powder bed fusion (L-PBF). We characterized the multi-layer specimens using laser confocal microscopy and SEM to obtain the macroscopic and microscopic microstructure, liquid metal embrittlement (LME) microcrack characteristics and precipitation evolution of the copper-steel fusion zone. The generation of liquid phase separation (LPS) was explored based on block specimens, and the textural characteristics of the fusion zone were analyzed using EBSD. As a result, because of multiple element precipitation and the high thermal conductivity of copper alloy, abrupt grain size changes occur in the fusion zone, affecting the fusion zone's corrosion resistance and nano-hardness. In tensile tests analyzing the anisotropy, the results show that LME microcracks have little impact on the interfacial bonding properties of the copper-steel bimetallic structure, among which the ultimate tensile strength of the specimens formed at 30° to the substrate reached a maximum of 562.9 MPa. These findings add substantially to our understanding of the relationship between the microstructure and properties of copper-steel bimetallic interface, and provide a theoretical reference for additive manufacturing copper-steel multi-material components.