Influence of Interfacial Sliding in Extrusion of Billet with Dissimilar Metals

Abstract

Cold extrusion is applied to produce a clad bar from an assembled billet where a core is inserted into a sheath. A hard–core billet was prepared with copper core and aluminum sheath, while a soft–core billet was prepared by swapping copper and aluminum arrangements. The billets with core diameter of 4mm, 6mm and 8mm were prepared under the outer diameter of 10.9mm. Two dies with different hole diameters were prepared to change the extrusion ratio. In this study, sliding between the core and the sheath was constrained by adding threads on the interface. Working conditions were limited by fracture of core or sheath. The soft–core billet had a wider working window in the extrusion ratio and the volume fraction of the core material to produce sound product when threaded. On the other hand, the working window of the hard–core was limited by sausaging and void formation at center in case of low extrusion ratio. Fracture of the sheath took place when the extrusion ratio was low and that the volume fraction of the core was high. It is concluded that the threads on the interface is effective to widen working limit of the soft–core materials.