Extrusion upsetting multiple processing in sandglass die

A new method of producing ultrafine grain sizes, known as extrusion upsetti ng multiple processing in sandglass die or sandglass extrusion, has been in vestigated using a Zn-5Al (wt-%) alloy. Since the shape of the test billet can remain unchanged after sandglass extrusion, the billet can be extruded repeatedly in order to obtain a large plastic strain. Ultrafine grain size can be achieved in the billet material due to the large plastic strain and dynamic recrystallisation during sandglass extrusion. The process technolog y, and the microstructures, superplasticity, and microhardness of the test material after sandglass extrusion have been studied. The experimental resu lts show that equiaxial ultrafine microstructures can be introduced into th e bulk test material during sandglass extrusion and high strain rate superp lasticity can be realised. (C) 2001 IoM Communications Ltd.