石墨电极-铜导线低温钎焊连接方法

设计一种石墨中温活性金属化和低温软钎焊方法，实现电导率传感器中石墨电极与漆包铜导线异质材料连接. 通过采用Ag-Cu-Ti合金焊膏实现对石墨表面进行真空活性金属化，再采用Sn-Ag合金药芯焊丝低温钎焊石墨金属层与漆包铜导线；利用金相显微镜、扫描电子显微镜、能谱仪对石墨金属层、石墨金属层/无氧铜反应界面的微观组织、相组成和元素扩散进行了分析，用万能拉伸机对石墨-无氧铜钎焊接头结合强度进行了测定. 结果表明，Ag-Cu-Ti合金焊膏在石墨表面作用明显，生成TiC化合物组成的反应层；留在石墨表面的钎料层，厚度约为60 μm；Sn-Ag合金钎料与石墨金属层润湿良好，润湿角为16°，中间反应层以Ag₃Sn金属间化合物为主；钎料与金属导线结合层由Cu₃Sn(ε相)和Cu₆Sn₅(η相)组成，钎焊接头抗拉强度为39 MPa，力学性能满足石墨电极与漆包铜导线连接可靠性的相关需求.

Method of the low temperature brazing connection between graphite electrode and copper conductor

A method of graphite medium temperature active metallization and low temperature soft brazing was designed to realize the connection between graphite electrode and enamelled copper conductor in the conductivity sensor. Ag-Cu-Ti alloy solder paste was used to realize vacuum active metallization of graphite surface, and then Sn-Ag alloy flux-cored wire was used to braze graphite metal layer and enameled copper wire at low temperature. The microstructure, phase composition and element diffusion of graphite-metal layer and graphite-metal layer/oxygen-free copper reaction interface were analyzed by means of metallographic microscope, scanning electron microscope and energy dispersive spectrometer, and the bonding strength of graphite - oxygen - free copper brazing joint was measured by universal stretcher. The result shows that Ag-Cu-Ti solder paste is combined with the graphite surface obviously, and the reaction layer of TiC compound is formed.The thickness of the solder layer left on the surface of graphite is about 60 μm. The metal layer between the Sn-Ag alloy solder and graphite presents good wettability, the wetting angle is 16°, the intermediate reaction layer is dominated by Ag₃Sn intermetallic compound. The bonding layer between solder and wire is composed of Cu₃Sn (ε phase) and Cu₆Sn₅ (η phase). The tensile strength of the brazed joint is 39 MPa, and the mechanical properties meet the reliability requirements of the connection between graphite electrode and enamelled copper wire.