Microstructures and microhardness of TA1/Q235B joints welded by TIG with Cu-based flux-cored wire

TA1/Q235B dissimilar butt and lap joints were obtained by tungsten inert gas (TIG) welding method with Cu-Cr-Co-Ni flux-cored wires. The microstructures of the joints were characterized by SEM, EDS and XRD. Microhardness tests were conducted to reveal the hardness distribution of the joints. The results showed that butt and lap welded joints were obtained without defects. Similar microstructures were observed in these two welded joints. Microstructure near TA1 interface consisted of β-Ti solid solution, FeTi and CuTi₂ compounds, and microstructure near Q235B consisted of Fe and Cu solid solution and Fe₂Ti compounds.The butt weld was composed of Cu solid solution, CuTi, Fe₂Ti, Cu₄Ti, τ₂ and τ₃ compounds. While in the lap joints, the weld was composed of Cu solid solution, τ₂ and Cu₄Ti compounds. The average hardness of the butt joint was 449 HV0.1, while that of the lap joint was 335 HV0.1.