Process optimization and fracture characteristic analysis of DP780 high strength steel weld-bonding

Based on Box-Behnken Design (BBD) method, experimental study on weld-bonding of DP780 high strength steel was carried out. The multiple regression equations between process parameters (welding current, welding time, electrode pressure) and response values (energy absorption value, failure load) were established, and the reliability of the model was verified by experiment. The result shows that welding current and welding time have a positive correlation with energy absorption value and failure load, while pressure has a negative correlation with energy absorption value and failure load. The optimum process parameters are welding current 8 kA, welding time 150 ms and electrode pressure 0.3 MPa. Under the corresponding parameters, the energy absorption value of the joint reaches 93.22 J, and the failure load reaches 17 688.46 N. Under static tension test conditions, there are two failure modes of weld-bonding joints: nugget pull-out and interface failure, and the former mode corresponds to higher energy absorption value and failure load. Fracture analysis shows that the fracture of nugget pull-out exhibits typical ductile fracture characteristics, and the fracture of the interface failure is characterized by cleavage fracture and complemented by ductile fracture.