Numerical studies of preheating time effect on temperature and material behaviours in friction stir welding process

The effect of preheating time on friction stir welding (FSW) is analysed in the current work by using a fully coupled thermomechanical model. Results indicate that the preheating time is very important for a successful FSW. Insufficient temperature rise and insufficient plastic deformation lead to the failure of FSW when the preheating time is very short. But excessive preheating time leads to the tool penetration in FSW. The rotating time of the material particles under the shoulder becomes longer when the preheating time is increased. Moreover, some of the material particles at the retreating side can enter into the advancing side when the preheating time is longer but this is not obvious when the preheating time is shorter. Based on this fact, it can be concluded that the decrease in the preheating time can lead to the decrease in the stirring effect of the welding tool, which may be the reason for the formation of the weld flaw when the preheating time is very short.