Deformation behavior and microstructural evolution of 7075-T6 aluminum alloy at cryogenic temperatures. (October 2016)

• Record Type: Journal Article
• Authors: Lee, Woei-Shyan; Lin, Ching-Rong
• Is Part Of: Cryogenics. Volume 79(2016)
• Page Start: 26
• Page End: 34
• Publication Date: 2016-10
• Subjects: 7075-T6 aluminum alloy -- Impact loading -- Flow behavior -- Grain -- Dislocation -- Microstructural evolution; Low temperature engineering -- Periodicals; Low temperature research -- Periodicals; 536.56
• DOI: 10.1016/j.cryogenics.2016.07.007
• Languages: English
• ISSNs: 0011-2275

Abstract

Highlights: 7075-T6 aluminum alloy is impacted at cryogenic temperatures ranging from 0 °C to −196 °C and strain rate in the range of 1 × 10 3 s −1 to 5 × 10 3 s −1 . The flow stress increases with increasing strain rate or decreasing temperature. The flow stress varies with the strain rate in accordance with a power law relation with an average exponent of 0.157 and an activation energy of 0.7 kJ/mol. The coupled effects of the strain rate and temperature on the flow stress are adequately described by the Zener-Hollomon parameter ( Z ). The higher flow stress is the result of a smaller grain size and higher dislocation density. Abstract: The impact deformation behavior and associated microstructural evolution of 7075-T6 aluminum alloy at cryogenic temperatures are investigated using a compressive split-Hopkinson pressure bar (SHPB) system. Cylindrical specimens are deformed at strain rates of 1 × 10 3 s −1, 2 × 10 3 s −1, 3 × 10 3 s −1 and 5 × 10 3 s −1 and temperatures of 0 °C, −100 °C and −196 °C. It is shown that the flow stress is strongly dependent on the strain rate and temperature. For a given temperature, the flow stress varies with the strain rate in accordance with a power law relation with an average exponent of 0.157 and an activation energy of 0.7 kJ/mol. Moreover, the coupled effects of the strain rate and temperature on the flow stress are adequately described by the Zener-Hollomon parameter (Z). For all test temperatures, catastrophic failure occurs only under the highest strain rate of 5 × 10 3 s −1, and is the result of adiabatic shear. An increasing strain rate or reducing temperature leads to a greater dislocation density and a smaller grain size. Finally, the dependence of the flow stress on the microstructural properties of the impacted 7075-T6 specimens is well described by a specific Hall-Petch constitutive model with constants of K = 108.3 MPa μm 1/2 and K ′ = 16.1 MPa μm, respectively. Overall, the results presented in this study provide a useful insight into the combined effects of strain rate and temperature on the flow resistance and deformability of 7075-T6 alloy and confirm that 7075-T6 is well suited to the fabrication of fuel tanks and related structural components in the aerospace field.