Wetting mechanism and microstructure evolution of TC4/304 stainless steel joined by CMT with an assisted hybrid magnetic field

To obtain excellent wettability under lower heat input, the role of external axial magnetic field was explored in wetting of liquid Cu on Ti and steel plate. The wetting activation energy decreased from 66 kJ/mol to 57.9 kJ/mol for the Cu/TC4 system, and from 78.9 kJ/mol to 51.8 kJ/mol for the Cu/304ss system when using a magnetic field, and the spreading limited factors changed from diffusion-limited to reaction-limited for the Cu/TC4 system. Besides this, the external axial magnetic field affected joint formation and interfacial microstructure: a wrap-around joint was formed on the Ti side and the spreading area of Cu on the steel plate surface was increased. A thick, continuous Ti2Cu3 and TiCu4 compound layer was transformed to a loose layer with multiple phases, consisting primarily of Cu, TiCu, Ti2Cu3, TiCu4, TiFe2, and Ti5Si3 therein. The Ti element segregated at the Cu/Fe interface and formed granular TiFe2 that was evenly distributed in the Fe-Cu solid solution, which transformed the original solid solution interface into a reaction interface. The highest tensile strength of 416 MPa increased by 44% compared to the joint without external magnetic field. (C) 2019 Elsevier B.V. All rights reserved.