Effect of Heat Exposure on the Fatigue Properties of AA7050 Friction Stir Welds

  • B. C. White
  • R. I. Rodriguez
  • A. Cisko
  • J. B. Jordon
  • P. G. Allison
  • T. Rushing
  • L. Garcia


This work examines the effect of heat exposure on the subsequent monotonic and fatigue properties of friction stir-welded AA7050. Mechanical characterization tests were conducted on friction stir-welded specimens as-welded (AW) and specimens heated to 315 °C in air for 20 min. Monotonic testing revealed high joint efficiencies of 98% (UTS) in the AW specimens and 60% in the heat-damaged (HD) specimens. Experimental results of strain-controlled fatigue testing revealed shorter fatigue lives for the HD coupons by nearly a factor of four, except for the highest strain amplitude tested. Postmortem fractography analysis found similar crack initiation or propagation behavior between the AW and HD specimens; however, the failure locations for the AW were predominantly in the heat-affected zone, while the HD specimens also failed in the stir zone. Microhardness measurements revealed a relatively uniform strength profile in the HD group, accounting for the variety of failure locations observed. The differences in both monotonic and cyclic properties observed between the AW and HD specimens support the conclusion that the heat damage (315 °C at 20 min) acts as an over-aging and a quasi-annealing treatment.


aluminum fatigue fracture friction stir welding heat damage 



A portion of this work was performed under the auspices of the U.S. Army Engineer Research and Development Center, administered by SOSSEC, INC, Subcontract No. 1006-14-1-1. The authors would like to recognize the efforts of the Edison Welding Institute in conducting the friction stir welding, as well as the microscopy resources provided by the Central Analytical Facility and its staff at the University of Alabama. Permission to publish was granted by Director, Geotechnical and Structures Laboratory.


  1. 1.
    M.C. Niu, Airframe Structural Design: Practical Design Information and Data on Aircraft Structures, Conmilit Press, Hong Kong, 2011Google Scholar
  2. 2.
    B.T. Gibson, D.H. Lammlein, T.J. Prater, W.R. Longhurst, C.D. Cox, M.C. Ballun, K.J. Dharmaraj, G.E. Cook, and A.M. Strauss, Friction Stir Welding: Process, Automation, and Control, J. Manuf. Process., 2014, 16(1), p 56–73. CrossRefGoogle Scholar
  3. 3.
    H.T. Kim and S.W. Nam, Solidification Cracking Susceptibility of High Strength Aluminum Alloy Weldment, Scripta Mater., 1996, 34(7), p 1139–1145. CrossRefGoogle Scholar
  4. 4.
    Z.J. Lu, W.J. Evans, J.D. Parker, and S. Birley, Simulation of Microstructure and Liquation Cracking in 7017 Aluminum Alloy, Mater. Sci. Eng., 1996, 220(1–2), p 1–7. CrossRefGoogle Scholar
  5. 5.
    J.-Q. Su, T. Nelson, R. Mishra, and M. Mahoney, Microstructural Investigation of Friction Stir Welded 7050-T651 Aluminum, Acta Mater., 2003, 51, p 713–729. CrossRefGoogle Scholar
  6. 6.
    R. Brown, W. Tang, and A.P. Reynolds, Multi-Pass Friction Stir Welding in Alloy 7050-T7451: Effects on Weld Response Variables and on Weld Properties, Mater. Sci. Eng., A, 2009, 514, p 115–121. CrossRefGoogle Scholar
  7. 7.
    M. Dixit, R.S. Mishra, and K.K. Sankaran, Structure-Property Correlations in Al 7050 and Al 7055 high-Strength Aluminum Alloys, Mater. Sci. Eng., A, 2008, 478(1–2), p 163–172. CrossRefGoogle Scholar
  8. 8.
    R. Fu, Z. Sun, R. Sun, Y. Li, H. Liu, and L. Liu, Improvement of Weld Temperature Distribution and Mechanical Properties of 7050 Aluminum Alloy Butt Joints by Submerged Friction Stir Welding, Mater. Des., 2011, 32, p 4825–4831. CrossRefGoogle Scholar
  9. 9.
    K.V. Jata, K.K. Sankaran, and J.J. Ruschau, Friction-Stir Welding Effects on Microstructure and Fatigue of Aluminum Alloy 7050–T7451, Metall. Mater. Trans. A, 2000, 31(9), p 2181–2192CrossRefGoogle Scholar
  10. 10.
    P.S. Pao, S.J. Gill, C.R. Feng, and K.K. Sankaran, Corrosion—Fatigue Crack Growth in Friction Stir Welded Al 7050, Scripta Mater., 2001, 45, p 605–612. CrossRefGoogle Scholar
  11. 11.
    R. John, K.V. Jata, and K. Sadananda, Residual Stress Effects on Near-Threshold Fatigue Crack Growth in Friction Stir Welds in Aerospace Alloys, Int. J. Fatigue, 2003, 25, p 939–948. CrossRefGoogle Scholar
  12. 12.
    L. Dubourg, A. Merati, and M. Jahazi, Process Optimisation and Mechanical Properties of Friction Stir Lap Welds of 7075-T6 Stringers on 2024-T3 Skin, Mater. Des., 2010, 31(7), p 3324–3330. CrossRefGoogle Scholar
  13. 13.
    J.Q. Su, T.W. Nelson, R. Mishra, and M. Mahoney, Microstructural Investigation of Friction Stir Welded 7050-T651 Aluminum, Acta Mater., 2003, 51(3), p 713–729. CrossRefGoogle Scholar
  14. 14.
    R.I. Rodriguez, J.B. Jordon, P.G. Allison, T. Rushing, and L. Garcia, Microstructure and Mechanical Properties of Dissimilar Friction Stir Welding of 6061-to-7050 Aluminum Alloys, Mater. Des., 2015, 83, p 60–65. CrossRefGoogle Scholar
  15. 15.
    G.E. Totten and D.S. MacKenzie, Handbook of Aluminum, Vol 1, M. Dekker, New York, 2003CrossRefGoogle Scholar
  16. 16.
    A. Fatemi, A. Plaseied, A.K. Khosrovaneh, and D. Tanner, Application of Bi-linear log-log S-N Model to Strain-Controlled Fatigue Data of Aluminum Alloys and Its Effect on Life Predictions, Int. J. Fatigue, 2005, 27(9), p 1040–1050. CrossRefGoogle Scholar
  17. 17.
    K. Piela, L. Blaz, Z. Sierpinski, and T. Forys, Non-isothermal annealing of AA7075 aluminum alloy-structural and mechanical effects, Arch. Metall. Mater., 2012, 57, p 703–709. CrossRefGoogle Scholar

Copyright information

© ASM International 2018

Authors and Affiliations

  • B. C. White
    • 1
  • R. I. Rodriguez
    • 1
  • A. Cisko
    • 1
  • J. B. Jordon
    • 1
  • P. G. Allison
    • 1
  • T. Rushing
    • 2
  • L. Garcia
    • 2
  1. 1.Department of Mechanical EngineeringThe University of AlabamaTuscaloosaUSA
  2. 2.Geotechnical and Structures LaboratoryUS Army Engineer Research and Development CenterVicksburgUSA

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