Dynamic recrystallisation and superplasticity in pure aluminium with zirconium addition

When commercial superplastic aluminium alloys were first under development it was concluded that to be successful the alloy should contain both a solid solution addition and a dispersion of fine, thermally stable dispersoids. In contrast to early beliefs, the present work demonstrates that a simple Al–1wt.%Zr alloy can exhibit good superplastic performance despite the absence of a solid solution element. The starting material was in the form of ∼1mm diameter particles produce via impulse atomisation that conferred a solidification rate ∼103Ks−1. After extrusion consolidation, heat treatment to produce a fine distribution of metastable Al3Zr precipitates, and rolling, the resulting sheet exhibited superplastic ductilities in excess of 500% at a strain rate of 10−1s−1. An EBSD study of the deformation behaviour demonstrated substantial grain refinement resulting from dynamic recrystallisation.