Effect of different lapping orders on mechanical performance and nugget forming process for three-sheet dissimilar resistance spot welding joints between DC06 and unequal-thickness hot-stamped B1500HS steel sheets

In this study, the mechanical properties of two welded joints under different lapping orders (B1500HS-1.4 mm/B1500HS-1.6 mm/DC06, denoted as type I; B1500HS-1.4 mm/DC06/B1500HS-1.6 mm, denoted type II) were compared. The nugget formation mechanism was analysed by a coupled electrical-thermal finite element model (FEM). It is found that different lapping orders significantly affect the mechanical properties of three-sheet RSW joints. All RSW joints tend to fail in the pull-out or tearing failure mode. The peak load of the two interfaces of type II RSW joint is more balanced, and the failure load of which is much higher than that of the type I RSW joint; The warpage was observed at type I welded joint. Considered the load-carrying capacity, type II was excellent. The simulation results indicate that the diameter of the weld nugget at the upper interface of the type I RSW joint was larger than that on the other interfaces, which agree well with the experimental results. The nugget formation mechanism of dissimilar high strength steel three-sheet RSW joint was obtained that forming the nugget firstly from two interfaces and final formed nuggets were asymmetric.