Fatigue Behavior of an Ultrafine-Grained Al-Mg-Si Alloy Processed by High-Pressure Torsion
Abstract
:1. Introduction
2. Experimental Section
3. Results and Discussion
3.1. Effect of HPT Processing on Microstructure of the Al 6061 Alloy
3.2. Effect of HPT Processing on Tensile and Fatigue Behavior of the Al 6061 Alloy
Processing | State | σ0.2 (MPa) | σUTS (MPa) | δ (%) | σf (MPa) | σf/σUTS | Reference |
---|---|---|---|---|---|---|---|
T6 | CG | 276 | 365 | 14 | 100 | 0.27 | present work |
HPT for 10 turns at RT | UFG | 605 | 675 | 5.5 | 200 | 0.30 | |
Т6 | CG | 275 | 310 | 12 | 97 | 0.31 | [34] |
ECAP at 125 °C for 1 pass | UFG | 310 | 375 | 20 | 80 | 0.21 | [21] |
ECAP at 100 °C, 4 passes | UFG | 386 | 434 | 11 | - | - | [33] |
ECAP + AA (130 °C for 24 h) | UFG | 434 | 470 | 10 | - | - | |
ECAP + CR (15%) | UFG | 470 | 500 | 8 | - | - |
3.3. Analysis of Fatigue Fracture Surfaces
4. Conclusions
- High-pressure torsion (HPT) of the Al 6061 alloy at room temperature leads to the formation of a very homogeneous ultrafine-grained (UFG) microstructure with an average grain size of 170 nm. The yield strength and ultimate tensile strength of the HPT processed alloy are increased as compared to the CG counterpart subjected to the conventional Т6 heat treatment from 276 MPa to 605 MPa and from 365 MPa to 675 MPa, correspondingly.
- HPT processing of the Al 6061 alloy improves its endurance limit by a factor of two (from 100 MPa after Т6 treatment to 200 MPa after HPT). This is related to the formation of a very homogeneous UFG microstructure with homogeneous resistance to fatigue crack initiation in the HCF regime. In the LCF regime, the UFG alloy shows somewhat lower fatigue resistance due to its lower strain hardening ability.
- Classical stages of fatigue crack initiation and propagation are clearly observed on the fatigue fracture surfaces of the CG T6-treated alloy and UFG alloy. Ductile striations are observed in the stage of stable crack propagation in the CG T6-treated alloy, whereas brittle striations seem to dominate on the fatigue fracture surface of the UFG alloy. The dimpled fracture surface is observed at the final stage of crack propagation in both material conditions, with dimples having a smaller size in the UFG alloy.
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Murashkin, M.; Sabirov, I.; Prosvirnin, D.; Ovid'ko, I.; Terentiev, V.; Valiev, R.; Dobatkin, S. Fatigue Behavior of an Ultrafine-Grained Al-Mg-Si Alloy Processed by High-Pressure Torsion. Metals 2015, 5, 578-590. https://doi.org/10.3390/met5020578
Murashkin M, Sabirov I, Prosvirnin D, Ovid'ko I, Terentiev V, Valiev R, Dobatkin S. Fatigue Behavior of an Ultrafine-Grained Al-Mg-Si Alloy Processed by High-Pressure Torsion. Metals. 2015; 5(2):578-590. https://doi.org/10.3390/met5020578
Chicago/Turabian StyleMurashkin, Maxim, Ilchat Sabirov, Dmitriy Prosvirnin, Ilya Ovid'ko, Vladimir Terentiev, Ruslan Valiev, and Sergey Dobatkin. 2015. "Fatigue Behavior of an Ultrafine-Grained Al-Mg-Si Alloy Processed by High-Pressure Torsion" Metals 5, no. 2: 578-590. https://doi.org/10.3390/met5020578