Abstract
Resistance spot welds (RSWs) in advanced high strength steels frequently exhibit interfacial failure during cross-tension testing: a mode of fracture associated with low-energy absorption. Automotive assembly lines include a paint application and baking cycle after the vehicle assembly and joining processes to cure paint and any adhesives used for assembly. In this article, the effects of a typical baking cycle: 180 °C for 20 min, on the failure mode and energy absorption during cross-tension testing of RSWs made in a TRIP1180 steel are reported. Further, short-time baking cycles of 30 s, 90 s, and 4 min were employed to investigate how quickly these baking effects are activated. RSWs, which exhibited interfacial failure and a low-energy absorption of 30.9 J in the as-welded condition, saw a change in a failure mode to partial interfacial failure and a 260% increase in energy absorption after baking for 30 s. After baking for a longer time (4 min), welds failed by button pull-out and exhibited a 296% increase in energy absorption during cross-tension testing. Baking for the full 20 min resulted in no additional improvement than was observed in the 4 min condition. The mechanisms responsible for the majority of the improvement in weld performance during baking are found to be activated after only 30 s of baking.
Microstructure and Mechanical Performance of Resistance Spot Welded Martensitic Advanced High Strength Steel