Development of a high strain rate superplastic Al-Mg-Zr alloy

For superplastic forming of aluminium to break out of the niche market that it currently occupies, alloys will be required to possess a higher strain rate capability, appropriate in service properties, and a significantly low er price and to be capable of volume production. This paper describes an ap proach that has been developed in an attempt to address these fundamental r equirements. A series of Al-Mg-Zr alloys with increasing levels of zirconiu m (0-1 wt-%) has been prepared via extrusion consolidation of cast particul ate (solidification rate similar to 10(3) K s(-1)). The superplastic proper ties of the resultant cold rolled sheet have been evaluated as a function o f thermomechanical treatment and zirconium addition. It has been found that increasing the level of zirconium has the twofold effect of improving the superplastic properties of the alloy while significantly decreasing the con comitant flow stress. At present the optimum superplastic behaviour has bee n obtained at strain rates of 10(-2) s(-1), with the 1%Zr material exhibiti ng ductilities in excess of 600%. The manufacturing route produces a bimoda l distribution of Al3Zr comprising >1 mum primary particles in combination with nanoscale solid state precipitates. The current postulation is that th is high strain rate superplasticity is conferred by a combination of partic le stimulated and strain induced recrystallisation. MST/4784.