Weld morphology and mechanical properties in laser spot welding of quenching and partitioning 980 steel

Abstract Quenching and partitioning (QP) steels offer excellent mechanical properties, which have shown a promise to reduce the vehicle weight and improve fuel economy. One of the bottlenecks for their applications in the automotive industry is the poor weldability. Laser spot welding (LSW) process was proposed in this study to join them in a lap joint configuration. It was found that the weld nugget size of laser spot welds was limited with fixed focus position due to the instability of laser beam energy. A novel method of laser spot welding process with real-time modulating the focus position was developed. Using the newly developed LSW process can significantly enlarge the weld diameter from 5.53 mm to 7.10 mm and improve the weld strength from 15.08 kN to 24.61 kN. The improvement in the weld diameter and the weld strength were attributed to increase in the irradiated area, which reduces the laser beam intensity and the materials loss. In addition, a high-speed camera was used to real-time monitor the laser spot welding process. Furthermore, the welds produced by newly developed laser spot welding process can generate the weld strength higher than RSW welds.