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The effect of grain size and temperature on the superplastic deformation behavior of a 7075 Al alloy

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Abstract

The high-temperature deformation behavior of a 7075 Al alloy has been investigated within the framework of a recently proposed internal-variable theory for structural superplasticity (SSP). The flow curves were obtained by performing a series of load relaxation tests for specimens with various grain sizes, at temperatures ranging from 445 °C to 515 °C. The overall flow curves were then separated into two parts, according to the respective physical mechanisms, viz., the grain-boundary sliding (GBS) and the accommodating dislocation glide processes, contrary to the conventional approach which uses a single power-law relation. These individual curves were then analyzed based on the internal-variable theory. Much valuable information has been obtained in this way, providing new physical insight as well as a more comprehensive understanding of SSP. The GBS curve could be described as a Newtonian viscous flow, signified by the power-index value of M g =1.0 for this alloy. The unresolved issue of threshold stress is also clarified and identified as a critical stress required for the GBS. The role of grain refinement is found to shift the grain-matrix deformation (GMD) curve into a higher stress and strain-rate region, while the GBS curve into a lower stress and higher strain-rate region along the respective characteristic scaling line to bring both curves into a common flow-stress region, in which the GMD and GBS can operate simultaneously, resulting in the usual superplastic deformation behavior.

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Authors and Affiliations

  1. Department of Materials Science and Engineering, the Pohang University of Science and Technology, 790-784, Pohang, Korea

    Yong Nam Kwon (Graduate Student)

  2. Center for Advanced Aerospace Materials, the Pohang University of Science and Technology, 790-784, Pohang, Korea

    Young Won Chang (Professor)

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  1. Yong Nam Kwon
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  2. Young Won Chang
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Kwon, Y.N., Chang, Y.W. The effect of grain size and temperature on the superplastic deformation behavior of a 7075 Al alloy. Metall Mater Trans A 30, 2037–2047 (1999). https://doi.org/10.1007/s11661-999-0014-z

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  • DOI: https://doi.org/10.1007/s11661-999-0014-z

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