摘要：Fully coupled thermo-mechanical model and modified Coulomb friction law are used to simulate the friction stir welding of AA 2024-T3 with thin and thick plates respectively. Comparison show that the material flow near the top surface is faster than the one near the bottom surface. The maximum velocity occurs in front of the welding pin in the retreating side on the top surface. This means that the effect of the shoulder on material flow is more obvious near the top surface. Higher power is needed when thick plates are friction stir welded. Friction dissipation is the main energy to consist of the heat source in friction stir welding. Higher proportion can be found in friction stir welding of thin plates to show that heat efficiency is higher. Plastic deformation and temperature are the main factors to affect the microstructures. The improvement of grains and the welding efficiency in friction stir welding of thick plates are weaker. Based on the energy results and the deduction on microstructural evolutions it can be found that higher efficiency occurs in friction stir welding of thick plates. © 2011 Journal of Mechanical Engineering.