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A predictive mechanism for dynamic strain ageing in aluminium–magnesium alloys

Nature Materials volume 5, pages 875–880 (2006)Cite this article

Abstract

Dynamic strain ageing (DSA) is the phenomenon in which solute atoms diffuse around dislocations and retard dislocation motion, leading to negative strain-rate sensitivity (nSRS) and thus to material instabilities during processing, an important issue in commercial metal alloys. Here, we show the mechanism of DSA and nSRS on experimental strain-rate, temperature and stress scales for Al–Mg to be single-atomic-hop motion of solutes from the compression to the tension side of a dislocation core. We derive an analytic expression for the strengthening versus strain rate and temperature that justifies widely used phenomenological forms, provides specific dependences of the parameters on material properties and is supported by atomistic kinetic Monte Carlo simulations. Using literature material properties, the predicted strengthening quantitatively agrees with the experimentally derived behaviour of Al–2.5% Mg at 300 K, and qualitatively agrees with the strain rate and temperature ranges of DSA and nSRS in Al–Mg alloys. The analyses herein show a clear path for multiscale design, from quantum to continuum mechanics, of solute strengthening in face-centred-cubic metal alloys.

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Figure 1: Binding energy of a Mg substitutional solute and an edge dislocation in Al versus Mg solute position.
Figure 2: Schematic diagrams of the core solute positions relative to a dislocation being driven to the right by an applied stress.
Figure 3: Contour map of Mg solute concentration after diffusion for a time Dbt/2b2=0.18 at 500 K as computed in the kMC model.
Figure 4: Change in binding energy (squares) and change in strength (circles) versus dimensionless time, as computed by kMC simulations at 300 K.
Figure 5: Strengthening parameter versus dislocation position during sliding.
Figure 6: Strength change versus strain rate over a range of temperatures (in K) as predicted by equation (8) (black lines), with parameters given in the text.

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Acknowledgements

The authors gratefully acknowledge support of this work by the General Motors/Brown Collaborative Research Laboratory on Computational Materials Science and the NSF Materials Research Science and Engineering Center on Micro and Nanomechanics of Materials at Brown University. W.A.C. thanks the John Simon Guggenheim Foundation for a fellowship, during which important components of this work were carried out, and C. Picu, B. Devincre and L. Kubin for discussions.

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Author notes

  1. David L. Olmsted

    Present address: Sandia National Laboratories, Albuquerque, New Mexico, 87185-1411, USA

Authors and Affiliations

  1. Division of Engineering, Brown University, Providence, Rhode Island, 02912, USA

    William A. Curtin & David L. Olmsted

  2. General Motors Technical Center, 30500 Mound Rd., Warren, Michigan, 48090-9055, USA

    Louis G. Hector Jr

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Correspondence to William A. Curtin.

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Curtin, W., Olmsted, D. & Hector, L. A predictive mechanism for dynamic strain ageing in aluminium–magnesium alloys. Nature Mater 5, 875–880 (2006). https://doi.org/10.1038/nmat1765

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