Abstract: Influence of temperature on mechanical properties of the 7075-T6 aluminum alloy sheet was studied by means of isothermal tensile tests. The microstructure change and fracture failure mechanism of the 7075-T6 aluminum alloy sheet during high temperature deformation were discussed by metallographic observation and fracture morphology analysis. The results show that with the increase of temperature, the strength and hardness of the material decrease gradually, and the elongation after fracture shows an upward trend with a low-lying level appears at 250 ℃. When the temperature is lower than 200 ℃, true stress increases rapidly with the strain and then grows slowly, during this process, strain hardening mechanism is dominant, and the main softening mechanism is dynamic recovery. As the temperature reaches 200 ℃, true stress keeps stable after the peak value, which is mainly attributed to balance between the strain hardening and the recovery softening processes. When the temperature exceeds 200 ℃, true stress increases rapidly to the peak with the strain and then gradually decreases. This is due to the contribution of dynamic re-crystallization to material softening. At 250 ℃, because the dynamic recrystallization softening dominates, the stress decreases and the plasticity decreases significantly. When temperature rises to 300 ℃, the re-crystallization process nearly completes, the grains are elongated along the tensile direction, the depth of dimples on the fracture surface increases, and their average sizes grow. In macroscopical sight, the plasticity of the material improves.

Key words: 7075-T6 aluminum alloy, isothermal tensile, mechanical properties, microstructure, fracture morphology