Analysis of Failure Modes of Resistance Spot Welded Dissimilar Thickness DP800/AISI 1040 Steel Joints: An Effect of Welding Current

This study analyzes the failure modes and fracture mechanisms of resistance spot welding (RSW) in dissimilar thickness DP800 and AISI1040 steels for automotive chassis applications. Shear fracture characteristics were examined by varying welding current parameters. The observed lap-shear failure modes in dissimilar joints included Pull-out fracture (PF), Interfacial (IF) failure, and Partial interfacial (P-IF) failure. Additionally, a correlation between welding current and fracture modes in dissimilar joints was established. The maximum shear fracture strengths observed were 23 kN for lap-tensile shear fracture load (L-TSFL) and 19 kN for cross-tensile shear fracture load (C-TSFL), both associated with pull-out fractures. Maximum hardness was recorded at the weld interface, reaching approximately 570 HV at a welding current of 6 kA. The changes in failure mode primarily resulted from severe stress concentration at the weld interface, with fluctuating microhardness also contributing to different failure modes in dissimilar joints.