Microstructure and properties of Q235 steel/6061 aluminum alloy resistance spot welding joint based on high-entropy alloy interlayer

The composite structure formed by steel and aluminum has a combination advantages of aluminums such as low density, high thermal conductivity, and excellent corrosion resistance, and hightlights of steels like high strength, toughness and low cost. The structure gives full play to the high performance of both materials and exhibits superior economic efficiency. However, it is difficult to obtain a reliable welding joint between the two materials due to the giant difference in the physical and chemical properties of them, which tend to generate brittle intermetallic compounds in the joint. In this paper, Fe_0.2CoCrMnNiAl_0.2 high-entropy alloy was applied as an interlayer to weld the steel/aluminum metals, utilizing the super solid solubility of the high-entropy alloy as a boost to the welding quality. The results show that when the interlayer was used, semi-elliptical nuggets showed up on the steel and aluminum sides of the joint section. The joint was neatly formed and without obvious macroscopic cracks, pores or other welding defects. The phase structures of the two nuggets were face-centered cubic solid solutions. The maximum tensile shear force of the joint reached 1913 N, which was 130% higher than that of the steel/aluminum direct resistance spot welded joint. Fracture occured at the aluminum alloy nugget, which was torn off by the tensile shear force and left on the surface of the high-entropy alloy, exhibiting a “button-like” fracture.