Abstract: Based on solid mechanics and finite element method a coupled thermo-mechanical model of the friction stir welding process is established, which serves as the basis for the further investigation on the effect of the preheating time on friction stir welding. The comparison with the experimental measured temperature and experimental observed material flow shows the validity and correctness of the established model. Numerical results show that the preheating time should be limited in the range of 1.000 s～3.281 s. When the axial freedom of the welding tool is controlled by the axial pressure, too short preheating time leads to the occurrence of void defect and too long preheating time leads to severe weld flash. The effective power needed for FSW will not be significantly changed by the variation of the preheating time. With the increase of the preheating time, the maximum temperature in friction stir welding is slightly increased and then the flow stress of the weld material is decreased accordingly, which can lead to the increase of the number of the material particles rotating with the welding tool. This phenomenon means that the stirring effect of the welding tool can become more obvious with the increase of the preheating time.

Key words: Finite element method, Friction stir welding, Preheating time, Thermo-mechanical analysis