Microstructures and performances of the butt joint of TA1/Q235B bimetallic sheet with addition of a Mo interlayer by using narrow gap laser welding with filler wire

Abstract

By taking molybdenum (Mo) having favorable metallurgical compatibility with both titanium and iron as the interlayer material, the butt joint of TA1/Q235B layered bimetallic sheet with thickness of 6 mm was prepared by utilizing narrow gap multi-pass laser welding with low heat input. Mo generally can favorably isolate Ti from Fe, meanwhile the transition zone of Mo and steel adjacent to Mo interlayer was softened according to the results of microhardness test. The results of face bending testing showed that the softened zone was beneficial to the mechanical properties of the welded joint, which could restrict the crack propagation along the interface of Mo/steel in fusion zone so that fracture appeared in the BM side. The microstructures of the softened zone exhibited a low dislocation density observed by a transmission electron microscope (TEM), which may be the main reason leading to a low microhardness. In additon, Mo interlayer was confined in a small zone, which only accounted for about 6.5% of the total area of cross section of the fusion zone while a small amount of FeTi and λ brittle intermetallic compounds (IMCs) still appeared around the Mo/steel interface in fusion zone. The tensile strength of the welded joint was 467 MPa, which took up about 93% that of base metal. The results of this paper will help guide endeavours for the fabrication of pipes and containers made of Ti/steel bimetallic sheets.