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Deformation behavior and microstructural evolution of 7075-T6 aluminum alloy at cryogenic temperatures.

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Title: Deformation behavior and microstructural evolution of 7075-T6 aluminum alloy at cryogenic temperatures.
Authors: Lee, Woei-Shyan1 wslee@mail.ncku.edu.tw, Lin, Ching-Rong1
Source: Cryogenics. Oct2016, Vol. 79, p26-34. 9p.
Subjects: Aluminum alloys, Deformations (Mechanics), Microstructure, Cryogenics, Hopkinson bars (Testing), Strain rate
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. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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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. [ABSTRACT FROM AUTHOR]
ISSN:00112275
DOI:10.1016/j.cryogenics.2016.07.007