  Ultrafine-grained aluminum alloys offer interesting multifunctional
properties with a combination of high strength, low electrical resistivity, and
low density. However, due to thermally induced grain coarsening, they typically
suffer from an intrinsic poor thermal stability. To overcome this drawback, an
Al-2%Fe alloy has been selected because of the low solubility of Fe in Al and
their highly positive enthalpy of mixing leading to the formation of stable
intermetallic particles. The two-phase alloy has been processed by severe
plastic deformation to achieve simultaneously submicrometer Al grains and a
uniform distribution of nanoscaled intermetallic particles. The influence of
the level of deformation on the microstructure has been investigated thanks to
transmission electron microscopy and atom probe tomography and it is shown that
for the highest strain a partial dissolution of the metastable Al6Fe particle
occurred leading to the formation of a Fe super saturated solid solution. The
thermal stability, and especially the precipitation of particles from the
ultrafine-grained solid solution and the way they pin grain boundaries has been
investigated both from static annealing and in-situ transmission electron
microscopy experiments. The correlation between microstructural features and
microhardness has been established to identify the various strengthening
contributions. Finally, it is 2 shown that ultrafine grained high purity Al
with less than 0.01 at. % Fe in solid solution could preserve a grain size only
300nm after 1h at 250$^\circ$C.
