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A calorimetric study of fatigue induced microstructural changes in aluminum alloy 7050

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Abstract

Differential scanning calorimetry (DSC) was used to detect microstructural changes resulting from strain-controlled fatigue of aluminum alloy 7050. Two starting conditions were investigated: a GP zone T6X temper and an overaged T73651. The calorimetric signature of the microstructure was determined for samples that had been cycled either to failure or to preselected percentages of their expected lifetime at various strain amplitudes. Thermodynamic and kinetic analyses of the calorimetric results revealed a pronounced effect of plastic strain during fatigue on the reaction enthalpy and reaction kinetics of the GP zone dissolution peak of T6X, and a lesser effect on theη′ dissolution peak of T73651. No microstructural changes after fatigue to failure in the nominally elastic strain regime were detected by DSC. The calorimetric results were uniform throughout the cross-section of the fatigue specimens. Based upon these results, it is concluded that approximately 75 pct of the GP zones initially present can be affected during low cycle fatigue, and that overaging of the GP zone microstructure does not occur. The results from the T73651 temper show that low cycle fatigue affects this overaged microstructure in a different manner. Reversion or disordering ofη′ does not occur, but some overaging was detected. It is suggested that theη′ precipitate in this alloy is not shearable.

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Authors and Affiliations

  1. Metals Science Laboratory Research Department, Grumman Aerospace Corporation, 11714, Bethpage, NY

    J. M. Papazian (Staff Scientist)

  2. Solid State Physics and Chemistry Branch Research Department, Grumman Aerospace Corporation, 11714, Bethpage, NY

    R. J. DeIasi (Branch Head)

  3. Metals Science Laboratory Research Department, Grumman Aerospace Corporation, 11714, Bethpage, NY

    P. N. Adler (Laboratory Head)

Authors
  1. J. M. Papazian
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  2. R. J. DeIasi
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  3. P. N. Adler
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Papazian, J.M., DeIasi, R.J. & Adler, P.N. A calorimetric study of fatigue induced microstructural changes in aluminum alloy 7050. Metall Trans A 11, 135–140 (1980). https://doi.org/10.1007/BF02700448

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  • DOI: https://doi.org/10.1007/BF02700448

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