Influence of fine scale features on room temperature superplastic behaviour of an ultrafine-grained Al-30Zn alloy

Two different ultrafine-grained states have been achieved in an Al-30Zn (wt%) alloy by high-pressure torsion (HPT) in different conditions. The material processed at room temperature exhibits a two phases mixture with Zn particles that have nucleated inside Al grains but also at triple lines and Zn segregation at grain boundaries. Under tensile stress at room temperature, this ultrafine grain structure gives rise to a superplastic behaviour with a total elongation exceeding 200%. Interestingly, further deformation by HPT at 50 degrees C leads to significantly finer intragranular Zn precipitates which affects the mechanical behavior reducing the elongation to failure down to only 70%. This transition in superplastic behaviour is attributed these fine scale Zn particles that should lead to a greater accumulation of dislocations and earlier failure. (C) 2019 Elsevier B.V. All rights reserved.