Effect of Thermal Exposure on Fatigue Properties of 7085 Aluminum Alloy

7085 aluminum alloy with T74 was exposed to heat at 80℃-240℃ for 5 h, and the microstructure, the fatigue properties after thermal exposure were analyzed and the relationship between them was built. The results show that the grain size of 7085-T74 aluminum alloy did not change significantly at the studied thermal exposure temperature. Within 120℃, the microstructure including precipitates and mechanical properties have no significant change. Above 120℃, with the increase of thermal exposure temperature, the average radius of[1](#fn-0002) precipitates increased significantly from 3.9 nm to 12.3 nm. The tensile strength and fatigue strength decreased conspicuously from 560MPa and 235MPa to 382MPa and 139MPa respectively. The fatigue life decreased from 10,000,000 cycles to 21,505 cycles under the load of 200 MPa when the thermal exposure temperature increased from room temperature to 240℃. In the range from room temperature to 240℃, the conditional fatigue strengths of the alloy under the fatigue life of 10 ⁶ cycles decreased from 242 MPa to 158 MPa. Furthermore, it is found that the fatigue strength is proportional to the -1/2 power of the precipitate size. In addition, the mechanism on the fatigue properties change after thermal exposure was discussed based on the microstructure variation.