Propagation of corrosion induced fatigue crack in aluminum alloy

Pawan Kumar; B B Verma; Pawan Kumar; B B Verma

doi:10.3934/matersci.2022030

AIMS Materials Science

2022, Volume 9, Issue 3: 512-521. doi: 10.3934/matersci.2022030

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Research article

Propagation of corrosion induced fatigue crack in aluminum alloy

Pawan Kumar ^{1
,
,},
B B Verma ²

1.
University of Johannesburg, Faculty of Engineering and the Built Environment, Department of Engineering Metallurgy, John Orr Building, DFC, 25 Louisa St, Doornfontein, Johannesburg, 2028, South Africa
2.
Department of Metallurgical and Materials Engineering, National Institute of Technology Rourkela 76908, India

Received: 05 March 2022 Revised: 23 May 2022 Accepted: 31 May 2022 Published: 27 June 2022

Aluminium is considered a green metal due to its environmental responsive characteristics. The 7475-T7351 aluminum alloy is extensively used in automotive and aerospace applications due to its light weight and high strength. In the present work, the effects of the corrosive environment on the high cycle fatigue (HCF) behaviors of the 7475-T7351 aluminum alloy was investigated. The aqueous solution of sodium chloride was used for solution treatment. The HCF test was performed on pre-cracked specimens using a servo-hydraulic universal testing machine, Instron 8800. The fractured specimens were characterized using a scanning electron microscope. It was observed that the crack propagation occurred through anodic dissolution at high stress and a significant crack tip blunting and crack extension occurred. However, no appreciable change in crack growth was noticed over the lower frequency range of 0.1 to 0.9 Hz. The slower growth rate envisages oxide debris formation between the cracked faces. When the alloy was treated under corrosive environments, the HCF tests depicted that the fatigue life reduces up to two orders of magnitude. The corrosion pits induced the crack initiation in stage-I at lower alternating stress; however, the fatigue crack growth rate (FCGR) was increased in the corrosive environment. The transition from stage-I to stage-II occurred at a lower stress intensity range (∆K) level; it was due to the combined effects of corrosion, hydrogen embrittlement, active path dissolution, and stress concentration. The corrosion fatigue test at low frequency also depicted a slower FCGR as compared to its moderate frequency counterpart and showed an irregular crack growth behavior.
- aluminium alloy,
- solution treatment,
- high cycle fatigue,
- microstructure
Citation: Pawan Kumar, B B Verma. Propagation of corrosion induced fatigue crack in aluminum alloy[J]. AIMS Materials Science, 2022, 9(3): 512-521. doi: 10.3934/matersci.2022030

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Abstract

Aluminium is considered a green metal due to its environmental responsive characteristics. The 7475-T7351 aluminum alloy is extensively used in automotive and aerospace applications due to its light weight and high strength. In the present work, the effects of the corrosive environment on the high cycle fatigue (HCF) behaviors of the 7475-T7351 aluminum alloy was investigated. The aqueous solution of sodium chloride was used for solution treatment. The HCF test was performed on pre-cracked specimens using a servo-hydraulic universal testing machine, Instron 8800. The fractured specimens were characterized using a scanning electron microscope. It was observed that the crack propagation occurred through anodic dissolution at high stress and a significant crack tip blunting and crack extension occurred. However, no appreciable change in crack growth was noticed over the lower frequency range of 0.1 to 0.9 Hz. The slower growth rate envisages oxide debris formation between the cracked faces. When the alloy was treated under corrosive environments, the HCF tests depicted that the fatigue life reduces up to two orders of magnitude. The corrosion pits induced the crack initiation in stage-I at lower alternating stress; however, the fatigue crack growth rate (FCGR) was increased in the corrosive environment. The transition from stage-I to stage-II occurred at a lower stress intensity range (∆K) level; it was due to the combined effects of corrosion, hydrogen embrittlement, active path dissolution, and stress concentration. The corrosion fatigue test at low frequency also depicted a slower FCGR as compared to its moderate frequency counterpart and showed an irregular crack growth behavior.

References

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