Development of superplasticity in an Al-Mg-Sc alloy

Superplasticity is the ability of polycrystalline materials to exhibit, in a relatively isotropic manner, large elongations prior to failure, under appropriate conditions of temperature and strain rate. This behaviour can be utilised in the shaping and forming of components, parts and structures that cannot be easily or economically produced from materials of normally limited ductility. Recent interest in replacing steel with aluminium in auto-body sheet-metal parts has led to Al-Mg based non-heat treatable alloys becoming potential candidates for automotive applications. In this work an Al-4wt.%Mg-0.25wt.%Sc alloy capable of exhibiting superplastic behaviour was developed. Using an appropriate casting schedule and a suitable thermomechanical processing route, fine-grained sheets of the alloy were produced. Tensile tests were carried out to characterize the high temperature deformation behaviour. It was demonstrated that the present alloy exhibits reasonably large elongations with a high sensitivity of the stress to the strain rate, typical of superplastic materials.