Excellent high strain rate superplasticity of Al-Mg-Sc-Zr alloy sheet produced by an improved asymmetrical rolling process

A fine-grained Al-6.10%Mg-0.30%Mn −0.25%Sc-0.1%Zr (wt. %) alloy with an average grain size of ∼1.10 μm was subjected to an improved asymmetrical rolling (ASR) process. Superplastic behavior of the asymmetrical rolled alloy was investigated at 450-500 °C and strain rate range of 5 × 10−3 s−1 to 2.5 × 10−1 s−1. It is indicated that the asymmetrical rolled alloy exhibited excellent superplasticity (elongations of >1000%) at high strain rates ranging from 1 × 10−2 s−1 to 2.5 × 10−1 s−1, and maximum elongation of ∼3170% was obtained at 500 °C and a high strain rate of 5 × 10−2 s−1. The microstructural results showed that the shear components and the β-fiber rolling texture gradually transferred into a random texture, and LABs progressively changed to HABs during deformation. Such a microstructure can accelerate the cooperative grain boundary sliding leading to a higher superplasticity. Further, superior superplastic behavior of the asymmetrical rolled alloy can be ascribed to the fine (sub)grains which may slow down the rate of cavity growth and the stable coherent Al3(Sc1-xZrx) nano-particles that can ensure a good stability of the fine-grained structure during superplastic deformation. Analyses on superplastic data and microstructure characteristic revealed that grain boundary sliding might be the main deformation mechanism during deformation.