In 7xxx Al-alloys (Al-Zn-Mg-Cu), the high mechanical strengths are obtained thanks to a fine dispersion of nanosized precipitates, ranging from GP zones formed at room temperature to $\eta$ phase formed at 120-160°C, which impede the motion of dislocations. Plastic deformation may strongly influence their precipitation kinetics. Dislocations accumulated during a pre-deformation step favour heterogenous nucleation, but also induce an acceleration of precipitation growth and coarsening via pipe diffusion [1]. During dynamic precipitation, when straining and precipitation occur simultaneously, the interactions between deformation and precipitates are more complex. It has been shown that the excess vacancies produced by the non-conservative movement of jogs during the deformation accelerate significantly the growth and coarsening processes at high temperature, through faster solute diffusion [1-3]. There are still few studies on dynamic precipitation at room temperature under monotonic deformation. Thus, the objective of this work is to understand the role of plastic deformation on the precipitation kinetics at room temperature. A heating tensile test device compatible with in situ small-angle X-ray scattering measurements (SAXS) is used for this work. SAXS is a very effective technique to study precipitation in 7xxx alloys because of the high electronic contrast between the precipitates and the matrix [4]. The evolution of the mean size and the volume fraction of the precipitates are obtained from the scattering signals during deformation. Tensile tests have been realized for varying initial states of precipitation (as-quenched, naturally aged and artificially aged samples) for an alloy AA7449 (8.3% Zn, 2.2 % Mg and 1.9% Cu, all in wt.%). The first results show that for the state with a high supersaturated solid solution, the plastic deformation increases the growth rate compared to a case without deformation (see Figure 1). This is probably due to the formation of excess vacancies during the deformation, which improve the solute diffusion. When the precipitation progresses towards equilibrium, this effect is first observed to diminish and eventually to reverse in T6 state, where a small but significant precipitate dissolution is observed to occur.

References
[1] A. Deschamps, G. Fribourg, Y. Bréchet, J. L. Chemin and C. R. Hutchinson: Acta Materialia, 2012, 60, 1905–1916.
[2] J. Robson, P. Jessner, M. Taylor and Z. Ma: Metall Mater Trans A, 2023, 54, 1131–1141.
[3] W.U. Mirihanage, J.D. Robson, S. Mishra, P. Hidalgo-Manrique, J.Q. da Fonseca, C.S. Daniel, P.B. Prangnell, S. Michalik, O.V. Magdysyuk, T. Connolley, M. Drakopoulos: Acta Materialia, 2021, 205, 116532.
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