Nonuniform Deformation in Cold Extrusion of Billet Assembled with Dissimilar Metals

Abstract

Clad materials are multi–materials with combined dissimilar metals. Clad materials exhibit unique properties that no monolithic materials show. In this study, cold extrusion was conducted to produce a clad bar from an assembled billet, where core was inserted in a sheath. A hard–core billet was prepared using copper for the core and aluminum for the sheath. By swapping copper and aluminum, a soft–core billet was also prepared. Under constant outer diameter of the billet, core diameter was varied 4mm, 6mm and 8mm. Two dies with different hole diameters were used to change the extrusion ratio. Working conditions to attain uniform deformation was limited by fracture of either core or sheath. As for the hard–core billets, core fraction was limited by sausaging and void formation at center in case of low extrusion ratio. Fracture of sheath took place when the extrusion ratio was small and the volume fraction was large. As for the soft–core billet, the core fraction to obtain uniform deformation was wider. However, the sheath showed fracture when the extrusion ratio was large and the core fraction was high.