Abstract: In order to simulate the deformation of metals in thermo-mechanically affected zone during friction stir welding,hot compression tests of LC9 aluminum alloy samples were performed on Gleeble-1500 machine,with a temperature ranging from 250℃~480℃ and strain rate ranging form 0.01s^-1~5s^-1.The results show that the thermo-mechanically affected zone of LC9 aluminum alloy in the friction stir welding weld is under the combined action of the heat and power.The deformational behavior can be simulated by hot compression tests in different deformation conditions.The relationship of flow stress with temperature and strain rate ofLC9 Aluminum Alloy can be described as .The microstructure and hardness of the thermo-mechanically affected zone of friction stir welding weld and the hot compression sample show the same characteristics,and this suggests that the constitutive equations of hot compression tests can be used to describe the material constitutive behavior and friction stir welding thermo-mechanically affected zone of LC9 aluminum alloy.