Investigation of the unloading yield effect in 7075 Al alloys based on microstructural and digital image correlation analysis

Howook Choi; Hwangsun Kim; Hye Jin Jeong; Eunjoo Shin; Wanchuck Woo; Sung Tae Hong; Myoung Gyu Lee; Heung Nam Han

doi:10.1016/j.matchar.2021.110963

Investigation of the unloading yield effect in 7075 Al alloys based on microstructural and digital image correlation analysis

Howook Choi, Hwangsun Kim, Hye Jin Jeong, Eunjoo Shin, Wanchuck Woo, Sung Tae Hong, Myoung Gyu Lee, Heung Nam Han

Research output: Contribution to journal › Article › peer-review

8 Scopus citations

Abstract

The unloading yield effect (UYE), which indicates that the reloading flow stress overshoots the monotonically loaded flow stress during uniaxial tensile test, was investigated by evaluating three aluminum alloy 7075 sheets with different precipitate states: solution heat-treated (SHT), aged for 20 min (A20, underaged), aged for 80 min (A80, peak aged) and aged for 240 min (A240, overaged). The precipitate states of A20 and A240 specimens were characterized by transmission electron microscope (TEM) and small-angle neutron scattering (SANS) analyses. The UYE was exhibited only in artificially aged specimens, but not in the SHT specimen. It was confirmed that the root cause of UYE is the interaction between the precipitate and dislocation during unloading. In addition, it was observed that strain instability is inevitably generated during stress overshoot owing to temporal geometric softening. The temporal strain instability diffused to the neighboring region in the case of A20 specimen, but that of A240 specimen directly influenced the premature localized necking or failure, resulting in a significant reduction in elongation.

Original language	English
Article number	110963
Journal	Materials Characterization
Volume	173
DOIs	https://doi.org/10.1016/j.matchar.2021.110963
State	Published - Mar 2021
Externally published	Yes

Funding

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2017M2A2A6A05017653 , 2018R1A2B6006856 , and 2020R1A5A6017701 ). H. Choi has been supported by POSCO Science Fellowship of POSCO TJ Park Foundation and KIAT for Graduate Educational Traineeship Program (No. P0002019 ) The Institute of Engineering Research at Seoul National University also provided research facilities for this work. MGL appreciates a partial support from KIAT (No. N0002598 ) for modeling Al alloy with finite element simulation.

Keywords

7075 aluminum alloy
Digital image correlation
Precipitate-dislocation interaction
Strain instability
Unloading yield effect

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10.1016/j.matchar.2021.110963

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title = "Investigation of the unloading yield effect in 7075 Al alloys based on microstructural and digital image correlation analysis",

abstract = "The unloading yield effect (UYE), which indicates that the reloading flow stress overshoots the monotonically loaded flow stress during uniaxial tensile test, was investigated by evaluating three aluminum alloy 7075 sheets with different precipitate states: solution heat-treated (SHT), aged for 20 min (A20, underaged), aged for 80 min (A80, peak aged) and aged for 240 min (A240, overaged). The precipitate states of A20 and A240 specimens were characterized by transmission electron microscope (TEM) and small-angle neutron scattering (SANS) analyses. The UYE was exhibited only in artificially aged specimens, but not in the SHT specimen. It was confirmed that the root cause of UYE is the interaction between the precipitate and dislocation during unloading. In addition, it was observed that strain instability is inevitably generated during stress overshoot owing to temporal geometric softening. The temporal strain instability diffused to the neighboring region in the case of A20 specimen, but that of A240 specimen directly influenced the premature localized necking or failure, resulting in a significant reduction in elongation.",

keywords = "7075 aluminum alloy, Digital image correlation, Precipitate-dislocation interaction, Strain instability, Unloading yield effect",

author = "Howook Choi and Hwangsun Kim and Jeong, {Hye Jin} and Eunjoo Shin and Wanchuck Woo and Hong, {Sung Tae} and Lee, {Myoung Gyu} and Han, {Heung Nam}",

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year = "2021",

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doi = "10.1016/j.matchar.2021.110963",

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T1 - Investigation of the unloading yield effect in 7075 Al alloys based on microstructural and digital image correlation analysis

AU - Choi, Howook

AU - Kim, Hwangsun

AU - Jeong, Hye Jin

AU - Shin, Eunjoo

AU - Woo, Wanchuck

AU - Hong, Sung Tae

AU - Lee, Myoung Gyu

AU - Han, Heung Nam

PY - 2021/3

Y1 - 2021/3

N2 - The unloading yield effect (UYE), which indicates that the reloading flow stress overshoots the monotonically loaded flow stress during uniaxial tensile test, was investigated by evaluating three aluminum alloy 7075 sheets with different precipitate states: solution heat-treated (SHT), aged for 20 min (A20, underaged), aged for 80 min (A80, peak aged) and aged for 240 min (A240, overaged). The precipitate states of A20 and A240 specimens were characterized by transmission electron microscope (TEM) and small-angle neutron scattering (SANS) analyses. The UYE was exhibited only in artificially aged specimens, but not in the SHT specimen. It was confirmed that the root cause of UYE is the interaction between the precipitate and dislocation during unloading. In addition, it was observed that strain instability is inevitably generated during stress overshoot owing to temporal geometric softening. The temporal strain instability diffused to the neighboring region in the case of A20 specimen, but that of A240 specimen directly influenced the premature localized necking or failure, resulting in a significant reduction in elongation.

AB - The unloading yield effect (UYE), which indicates that the reloading flow stress overshoots the monotonically loaded flow stress during uniaxial tensile test, was investigated by evaluating three aluminum alloy 7075 sheets with different precipitate states: solution heat-treated (SHT), aged for 20 min (A20, underaged), aged for 80 min (A80, peak aged) and aged for 240 min (A240, overaged). The precipitate states of A20 and A240 specimens were characterized by transmission electron microscope (TEM) and small-angle neutron scattering (SANS) analyses. The UYE was exhibited only in artificially aged specimens, but not in the SHT specimen. It was confirmed that the root cause of UYE is the interaction between the precipitate and dislocation during unloading. In addition, it was observed that strain instability is inevitably generated during stress overshoot owing to temporal geometric softening. The temporal strain instability diffused to the neighboring region in the case of A20 specimen, but that of A240 specimen directly influenced the premature localized necking or failure, resulting in a significant reduction in elongation.

KW - 7075 aluminum alloy

KW - Digital image correlation

KW - Precipitate-dislocation interaction

KW - Strain instability

KW - Unloading yield effect

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Investigation of the unloading yield effect in 7075 Al alloys based on microstructural and digital image correlation analysis

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Keywords

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