Forming Quality of Cu/Ni Microfilaments Joints by Using Parallel Electrodes Micro-Resistance Brazing

To address the challenges associated with precision bonding between micro-wires of sensors and high-temperature conductors, this work realizes the brazing connection of Cu/Ni micro-wires through a self-developed parallel electrode micro-resistance brazing method. A systematic investigation was conducted on the influence of welding time and current on the macro-morphology, microstructure, and mechanical properties of the brazed joints, revealing the intrinsic relationship between process parameters, microstructure, and mechanical properties. The results indicate that extending the welding time improves the wettability of the filler metal. However, when the welding time exceeds 120 ms, the Ni substrate is prone to melting through. Furthermore, when the welding current is too low, the filler metal will not melt sufficiently, whereas when it is too high, the base metal will melt through. Under the optimal parameter combination (1.0 kA/120 ms), the joint exhibits well-formed morphology with a tensile strength of 17.27 N (89.7% of the original Cu base metal strength). Fracture occurs in the heat-affected zone of the Cu substrate, displaying multi-stage ductile-brittle mixed fracture characteristics. The joint cross-section exhibits a dense dendritic grain structure, with the Ni-CuPAg interface forming an effective strengthening layer due to the precipitation of the hard Ni₃P phase (hardness:263 HV). This study defines the control boundaries for welding time and current, providing theoretical foundations and technical support for the precise control of micro-wire brazing processes.