Microstructure and mechanical properties of S45C steel prepared by laser-assisted friction stir welding

In this study, a laser heating system was used as a preheating source during the friction stir welding of 3.2 mm thick S45C steel plates. The position of the laser focal point exerted a different preheating effect on the microstructure and mechanical properties of the welds. When the laser beam was focused just at the joint line and 10 mm ahead of the rotating tool, the maximum welding speed can reach 800 mm/min, which is much higher than that of 400 mm/min during the normal FSW process. In addition, the formation of a brittle martensite phase can also be prevented by preheating when the welding speed is less than 600 mm/min. It was also found that preheating on the advancing side can significantly reduce the frictional heat between the tool and the workpiece. However, preheating on the retreating side can result in highest total heat input into the workpiece.