Deformation and Creep Characteristics of AA7075-T76 at Elevated Temperatures

In this work, deformation behavior as well as creep and cavitation of AA7075-T76 were studied. The as-received plate was first stabilized utilizing solution treatment followed by two-stage artificial aging at 120 and 180 °C. Then, tensile tests were carried out on the aged-alloy in the temperature range between 120 and 250 °C under strain rates of 0.0005 and 0.005 s⁻¹. Furthermore, stress-controlled creep tests were performed at temperatures varying between 120 and 210 °C at stresses ranging from 130 to 250 MPa. Microstructural evolution was then conducted to assess the microstructural changes and growth of cavities during creep employing optical metallography and scanning electron microscopy. The results showed that softening mechanisms during deformation were operative at about 210 °C resulting considerable strain rate sensitivity. The creep activation energy was computed as 164.5 kJ/mole at a constant stress of 170 MPa. Meanwhile, the stress exponent was found to be about 5.7 indicating that dislocation climb could be the main creep mechanism under the examined conditions. Both types of cavity growth mechanisms, namely diffusion-controlled and strain-controlled, were found to be operative during creep. Also, the phenomenon of cavity coalescence was detected at temperature 150 °C at 170 and 190 MPa after 4 and 3 days, respectively, leading to pseudo-brittle fracture.