Thermal–Mechanical Analysis of Welding Deformation and Residual Stress in TS1500/SPC1180 Lap Joints Using Cold Metal Transfer Welding

The ongoing requirement for the lightweight design of automotive resulted in the wide application of ultra-high-strength steel (UHSS), such as the 1500 MPa made by hot stamping (TS1500) and 1180 MPa manufactured by cold rolling (SPC1180). In the present research, cold metal transfer (CMT) lap welding was employed to join TS1500 and SPC1180 dissimilar metals. A thermal–mechanical coupled model was developed, and the associated behaviors that occurred in CMT process were reproduced efficiently by the in-house FE code JWRIAN-Hybrid. The high-temperature material properties of TS1500 were clarified. The predicted temperature field, residual stress distribution and welding deformation were verified experimentally. The analyzed and measured results showed good agreement with each other. The critical phase transformation temperatures of TS1500, including Ac1, Ac3 and Ms, were gauged as 740, 810 and 390 °C, respectively. On the UHSS welded joint, the largest tensile stress was located on the outside of heat affected zone on TS1500 sheet, which can reach about 650 MPa, while the peak on SPC1180 sheet was only 120 MPa. It presented the significant influence of both material strength and constraint conditions. There was a compressive stress about − 130 MPa at the weld zone due to the martensite transformation. The out-of-plane deformation modes were the convex shape in both the longitudinal and transverse directions. The maximum out-of-plane displacement-Z in the center of welded joint was about 1.38 mm. For the UHSS CMT welded lap joint, the strength grade of steel couple had a significant effect on welding deformation rather than the residual stress.