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Influence of Heat Treatment on Near-Threshold Fatigue Crack Growth Behavior of High Strength Aluminum Alloy 7010

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Abstract

In this study, aluminum alloy 7010 was subjected to three different ageing treatments i.e., peak ageing (T6), over ageing (T7451) and retrogression and re-ageing (RRA) to study the influence of precipitate microstructure on the fatigue crack growth rate (FCGR) behavior. The microstructural modifications were studied by using TEM to examine the change in size and morphology of the precipitates. The size of the precipitates in the matrix range from 16–20 nm in T7451, 5–6 nm in RRA and 2–3 nm in T6 alloys, respectively. The FCGR tests were performed on standard compact tension (CT) specimens as per ASTM E647 standard in a computer controlled servo-hydraulic test machine with applied stress ratio, R = 0.1 and loading frequency of 10 Hz. The crack growth was measured by adopting compliance technique using a CMOD gauge attached to the CT specimen. The fatigue crack growth rate was higher in T7451 and lowest in RRA treated alloy. The RRA treated alloy showed higher ∆Kth compared to T7451 and T6 treated alloys. The measured ∆Kth was 11.1, 10.3 and 5.7 MPam½ in RRA, T6 and T7451 alloys, respectively. In the near-threshold regime, the RRA treated alloy exhibited nearly 2–3 times reduction in the crack growth rate compared to the T6 alloy. The growth rate in the RRA alloy was one order lower than that of the T7451 condition. The surface roughness of RRA treated alloy was more pronounced. The reduction in FCGR observed in RRA alloy was correlated to partial crack closure due to tortuous crack path and partially due to increased spacing between the matrix precipitates. The reduction in near-threshold FCGR and increase in ∆Kth is expected to benefit the damage tolerant capability of the aircraft structural components under service loads.

Keywords

  • Damage tolerance
  • Fatigue
  • Heat treatment
  • Microstructure
  • RRA

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Acknowledgements

All the authors would like to thank the Director NITK and the Director CSIR-NAL for the support provided during the research work.

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Correspondence to C. M. Manjunatha .

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Nandana, M.S., Udaya, B.K., Manjunatha, C.M. (2020). Influence of Heat Treatment on Near-Threshold Fatigue Crack Growth Behavior of High Strength Aluminum Alloy 7010. In: Niepokolczycki, A., Komorowski, J. (eds) ICAF 2019 – Structural Integrity in the Age of Additive Manufacturing. ICAF 2019. Lecture Notes in Mechanical Engineering. Springer, Cham. https://doi.org/10.1007/978-3-030-21503-3_35

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  • DOI: https://doi.org/10.1007/978-3-030-21503-3_35

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  • Publisher Name: Springer, Cham

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  • Online ISBN: 978-3-030-21503-3

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