Microstructure and properties of copper/steel TIG welded joint based on high-entropy alloy interlayer

Key words:  T2 copper  Q235 steel  TIG welding  high-entropy alloy interlayer  microstructure  properties

Abstract:

The copper/steel composite structure can not only meet the performance requirements of different environments, but also can reduce the consumption of copper materials and greatly reduce the cost of components. However, the physical and chemical properties of copper and steel are quite different, and the extremely poor miscibility will lead to liquid phase separation or defects after welding. Based on the idea of solid solution-high entropy of weld metal, Fe₅Co₃₀Cr₃₀Ni₃₀Cu₅ high-entropy alloy was designed as the intermediate layer to carry out TIG welding of T2 copper and Q235 steel, and the microstructure and properties of the intermediate layer and welded joint were analyzed. The results show that, Fe₅Co₃₀Cr₃₀Ni₃₀Cu₅ high-entropy alloy is a single-phase FCC solid solution with good strength and plastic toughness. Using the high-entropy alloy as the intermediate layer material, the reliable connection between T2 copper and Q235 steel can be achieved by the TIG welding method. The welded joint is formed well, without pores, cracks and other defects. The weld microstructure is a simple solid solution with FCC structure, which has a remarkable high entropy characteristic. The average tensile strength value of the welded joint is 225 MPa, reaching 91% of the strength of T2 copper, and the extension ratio after fracture can reach 44%. The fracture of joint occurs in the heat-affected zone on the copper side. There are a large number of dimples on the fracture surface, showing the significant characteristic of ductile fracture.