Improved fatigue crack growth resistance by retrogression and re‐aging heat treatment in 7010 aluminum alloy

Aircraft grade 7010 aluminum alloy was heat treated to two different conditions: (1) standard peak aging (T6) and (2) retrogression and re‐aging (RRA). The microstructures of these alloys were characterized by using transmission electron microscope. Fatigue crack growth rate (FCGR) tests were conduc...

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Bibliographic Details
Published in:Fatigue & fracture of engineering materials & structures 2019-03, Vol.42 (3), p.719-731
Main Authors: Nandana MS, Udaya Bhat K, Manjunatha, C M
Format: Article
Language:English
Subjects:
7010 aluminum alloy
Aging
Aging (metallurgy)
Alloys
Aluminum alloys
Aluminum base alloys
Chemical precipitation
Compact tension
Crack closure
Crack propagation
fatigue crack growth
Fatigue failure
Fatigue tests
Fracture mechanics
Grain boundaries
Heat treatment
Metal fatigue
near‐threshold
Precipitates
retrogression
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Summary:Aircraft grade 7010 aluminum alloy was heat treated to two different conditions: (1) standard peak aging (T6) and (2) retrogression and re‐aging (RRA). The microstructures of these alloys were characterized by using transmission electron microscope. Fatigue crack growth rate (FCGR) tests were conducted using standard compact tension specimens, following ASTM standards. Tests were conducted at various stress ratios, R ranging from 0.1 to 0.7. The RRA‐treated alloy was observed to contain coarsened η′ (MgZn2) precipitates with higher inter‐particle spacing when compared with T6‐treated alloy. The grain boundary precipitates (GBPs) were also coarsened and discontinuous in RRA‐treated alloy as compared with continuous GBPs in T6 condition. The FCGR was lower and ΔKth was higher in RRA‐treated alloy compared with T6‐treated alloy at all the stress ratios investigated. Improved fatigue crack growth resistance in RRA‐treated alloy was correlated to the modified microstructure and enhanced crack closure levels.
ISSN:8756-758X
1460-2695
DOI:10.1111/ffe.12946