Microstructure and property of fusion welding butt joints of TA2/Q235 composite plate with Ni alloy transition layers

Fusion welding of TA2/Q235 composite plate was carried out by taking Ni alloy as filled material. The microstructure, chemical, phase composition and mechanical properties of the weld metal were investigated. Results showed that the microstructure of TA2 coating was mainly lath α-phase and microstructure of Q235 matrix was massive pearlite and ferrite near the weld zone. In the weld, microstructure of Ti layer was mainly a dendritic growth of β-phase, containing NiTi₂, Ni₃Ti, TiFe, TiFe₂ and TiCr₂. Microstructure of Ni alloy layer was mainly γ-Ni, and contained a small amount of Fe₃Ni₂, CrNi₂ and (CrNiMo) compounds. Between Ti layer and Ni layer, there was a transition layer width of 50 μm , and a lot of needle were in the transition layer such as NiTi₂ and NiTi intermetallic compound coated by CrNi₂ phase. From the Ti layer to the Ni alloy layer, element Ti decreased slowly, Ni increased first and then decreased and Cr, Mo element increased slowly. The intermetallic and brittle phases in the Ti layer and the transition layer increased the hardness and reduced the ductility.