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Influence of Backpressure During ECAP on the Monotonic and Cyclic Deformation Behavior of AA5754 and Cu99.5

Authors

  • Andreas Böhner,

    Corresponding author
    1. Department of Materials Science and Engineering, Institute 1: General Materials Properties, University of Erlangen-Nürnberg, D-91058 Erlangen, (Germany)
    • Department of Materials Science and EngineeringInstitute 1: General Materials Properties, University of Erlangen-Nürnberg, D-91058 Erlangen, (Germany).
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  • Florian Kriebel,

    1. Department of Materials Science and Engineering, Institute 1: General Materials Properties, University of Erlangen-Nürnberg, D-91058 Erlangen, (Germany)
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  • Rimma Lapovok,

    1. Materials Engineering Department, Monash University, CoE for Design in Light Metals, Clayton, Vic 3800, (Australia)
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  • Heinz Werner Höppel,

    1. Department of Materials Science and Engineering, Institute 1: General Materials Properties, University of Erlangen-Nürnberg, D-91058 Erlangen, (Germany)
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  • Mathias Göken

    1. Department of Materials Science and Engineering, Institute 1: General Materials Properties, University of Erlangen-Nürnberg, D-91058 Erlangen, (Germany)
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  • The authors would like to thank Mathis Ruppert, who investigated parts of the monotonic behavior shown here in his student work and also acknowledge gratefully the Deutsche Forschungsgemeinschaft (DFG) for funding this work within the Forschergruppe FOR 544.

Abstract

Ultrafine-grained (UFG) metals produced by equal channel angular pressing (ECAP) exhibit outstanding mechanical properties. They show high strength under monotonic loading as well as strongly enhanced fatigue lives in the Wöhler S–N-plot compared to their coarse grained (CG) counterparts. It could be shown that the fatigue lives can be significantly enhanced further by applying backpressure during ECAP. Besides the positive effect of backpressure on the processability of hard to deform materials via ECAP, the hydrostatic stress induced by backpressure also influences the mechanical properties under monotonic and cyclic loading. Therefore the influence of backpressure on ECAPed Cu99.5 and on the ECAPed aluminum alloy AA5754 was investigated. It is shown that backpressure has no effect on the hardness and grain size in Cu99.5 but changes the grain boundary misorientation to higher fractions of low angle grain boundaries. Also the temperature dependency of the yield strength as well as the hardening behavior under monotonic compression is affected. The cyclic deformation behavior of Cu99.5 is not strongly influenced by backpressure, but the mean stress level changes drastically. The fatigue life increases with the application of backpressure at low plastic amplitudes due to a change in the crack initiation and propagation.

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