Symbiosis between grain boundary sliding and slip creep to obtain high-strain-rate superplasticity in aluminum alloys

Aluminum alloys with a fine and recrystallized microstructure deform by grain boundary sliding at low strain rates. However, some aluminum alloys, for instance, Al–5% Ca–5% Zn, Supral 2004, Al–Li 2090, Al–Li 8090, show indications of slip creep and grain boundary sliding at a given temperature and strain rate inside the superplastic range. These materials, in addition, deform superplastically even at high-strain rates (10−2 to 10−1 s−1). The simultaneous operation of grain boundary sliding (GBS) and slip creep is a surprising observation since these two deformation mechanisms usually act independently of one another. The one yielding the highest strain rate becomes rate controlling and thus the main contributor to the total strain. In this paper, microstructure (including microtexture) as well as mechanical property data of several Al alloys are reviewed with the aim of seeking further understanding on the symbiosis between GBS and slip creep.