A homogenized, supersaturated AlZnMgZr alloy was processed via severe plastic deformation
(SPD) using a high-pressure torsion (HPT) technique for different revolutions at room
temperature to obtain an ultrafine-grained (UFG) microstructure. The microstructure
and mechanical properties of the UFG samples were then studied using transmission
electron microscopy (TEM), differential scanning calorimetry (DSC), and tensile and
hardness measurements. The main purpose was to study the effect of shear strain on
the evolution of the microstructure of the investigated alloy. We found a very interesting
evolution of the decomposed microstructure in a wide range of shear strains imposed
by HPT. While the global properties, such as the average grain size (~200 nm) and
hardness (~2200 MPa) appeared unchanged, the local microstructure was continuously
transformed. After 1 turn of HPT, the decomposed UFG structure contained relatively
large precipitates inside grains. In the sample processed by five turns in HPT, the
segregation of Zn atoms into grain boundaries (GBs) was also observed. After 10 turns,
more Zn atoms were segregated into GBs and only smaller-sized precipitates were observed
inside grains. The intensive solute segregations into GBs may significantly affect
the ductility of the material, leading to its ultralow-temperature superplasticity.
Our findings pave the way for achieving advanced microstructural and mechanical properties
in nanostructured metals and alloys by engineering their precipitation and segregation
by means of applying different HPT regimes.
