Microstructure and Mechanical Properties of TA2/Q235 Laser Weld Joint with Copper Interlayer

Abstract

For the dissimilar metal welding needs of TA2 titanium and Q235 steel, preliminary trials were conducted using laser welding methods, and the results showed that the addition of a copper interlayer and the bias of the laser beam toward the Q235 side allowed for an effective connection. The welding temperature field was simulated using the finite element method, and the optimum offset distance of 0.3 mm was obtained. Under the optimized parameters, the joint had good metallurgical bonding. Further SEM analysis showed that the microstructure of the bonding area between the weld bead and Q235 was a typical fusion weld pattern, while that of the bonding area between the weld bead and TA2 was in brazing mode. The microhardness of the cross-section showed complex fluctuations; the microhardness of the weld bead center was higher than that of the base metal due to the formation of a mixture microstructure of copper and dendritic Fe phases. The copper layer not involved in the weld pool mixing had almost the lowest microhardness. The highest microhardness was found at the bonding site of TA2 and the weld bead, mainly due to the formation of an intermetallic layer with a thickness of about 100 μm. Further detailed analysis revealed that the compounds included Ti2Cu, TiCu and TiCu2, showing a typical peritectic morphology. The tensile strength of the joint was approximately 317.6 MPa, reaching 82.71% of that of the Q235 and 75.44% of the TA2 base metal, respectively. The fracture occurred in the unmixed copper layer.

Laser Welding of Titanium/Steel Bimetallic Sheets with In Situ Formation of Fex(CoCrNiMn)Tiy High-Entropy Alloys in Weld Metal

“…The main reason for the increase in the strength value of the welded joint may be attributed to the decrease in Ti content in the WM. Nonetheless, the strength value is lower compared to the experimental results of Zhang et al [32]. It may have a close relationship with the presence of large welding defects in this study.…”

“…Epitaxial solidification is observed as the grains in the weld edge grow attached to the Q345 boundary. The grains display directionality towards the WM and feature characteristic columnar crystal morphology [32]. According to the results from Sokkalingama et al [33], the growth of columnar crystals is directly influenced by the rate of heating and cooling.…”

“…Zhang et al [10] found that joint strength can reach ~467 MPa due to the presence of an Fe-based solid solution in the WM. Moreover, Zhang et al [32] found that a joint strength of ~317.6 MPa can be achieved for the fusion brazing of TA2/Q235 bimetallic sheets. It is noteworthy that the presence of solid solutions, rather than IMCs, in the WM can significantly improve the tensile strength of the welded joints of Ti/steel bimetallic sheets.…”