TUNING THE STRUCTURE AND THE MECHANICAL PROPERTIES OF ULTRAFINE GRAIN Al-Zn ALLOYS BY SHORT TIME ANNEALING.

Solid solution treated Al-Zn alloys with different Zn contents (10 and 30 wt.%) have been nanostructured by severe plastic deformation (SPD) via equal-channel angular pressing method. In-situ transmission electron microscopy observations have been used to follow microstructure evolutions upon annealing. It was shown that SPD leads to the precipitation of Zn particles and that this partial solid solution decomposition was more pronounced in the Al- 30%Zn alloy. Annealing at temperatures in range of 200 to 250 °C led to visible dissolution of Zn particles in both alloys and to formation of extensive grain boundary segregations of Zn. This approach helped to design short term annealing treatments leading to specific ultrafine grain structures that could be achieved by static annealing on bulk samples. Last, the tensile behavior of these materials has been investigated with a special emphasis on the influence of the strain rate on the yield stress and on the elongation to failure. It is shown that in any case the yield stress is mainly controlled by the grain size, while a low volume fraction of Zn phase leads to a relatively modest ductility. [ABSTRACT FROM AUTHOR]