High strain rate superplasticity in a continuously recrystallized Al-6%Mg-0.3%Sc alloy

The superplastic properties of a cold-rolled Al-6Mg-0.3Sc alloy were studied at temperatures between 450 and 560 degrees C and strain rates between 10(-4) and 10(0) s(-1). The alloy was observed to exhibit super plasticity over wide temperature (475-520 degrees C) and strain rate ranges (similar to 10(-3)-10(-1) s(-1)). It was found that the addition of Sc to AI-Mg alloys resulted in a uniform distribution of fine coherent Al3Sc precipitates which effectively pinned subgrain and grain boundaries during static and dynamic recrystallization. In this paper, the microstructural evolution during superplastic deformation was systematically examined using both optical and transmission electron microscopy. Based upon this microstructural examination, a mechanism is proposed to explain the observed high strain rate superplasticity in the alloy. A model is also proposed that describes grain boundary sliding accommodated by dislocations gliding across grains containing coherent precipitates. (C) 1998 Acta Metallurgica Inc.