中文摘要：

基于固体力学的有限元方法建立搅拌摩擦焊接过程的热力耦合分析模型,并以此为基础,研究预热时间对搅拌摩擦焊接过程的影响,与试验测量的温度和试验观测到的材料流动现象的对比证明了该模型的有效性和正确性。数值模拟结果显示预热时间需要控制在1.000～3.281s之间,在采用压紧力控制搅拌头轴向自由度的情况下,预热时间过短会导致孔洞缺陷的形成,而预热时间过长会导致飞边现象变得非常严重。搅拌摩擦焊接所需的有效功率不会随预热时间的变化发生明显改变。随着预热时间的延长,搅拌摩擦焊接中的最高温度略有增加,同时,焊接材料温度的升高使材料的流动应力下降,导致随搅拌头一起流动的物质点略有增加,说明搅拌头的搅拌效应随着预热时间的延长而变得明显。

英文摘要：

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 1 cad 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.