Formation and utilization of compound billet

Abstract

Methods are disclosed for the formation and utilization of a compound billet wherein a longitudinally extending inner member, composed of a first material, is retained firmly within the interior of a hollow, longitudinally extending outer member, composed of a second material, and wherein relaxation strain characteristic of the second material is greater than the relaxation strain characteristic of the first material. Such a compound billet is formed by providing a billet blank, wherein a longitudinally extending inner element, composed of the first material, resides within a hollow, longitudinally extending outer element, composed of the second material; applying to the longitudinal ends of the inner element a longitudinal stress of a magnitude sufficient to cause the inner element to deform plastically outwardly, perpendicularly to the direction of its longitudinal extension, to such an extent as to cause the outer element also to deform plastically outwardly, perpendicularly to such direction of longitudinal extension; and then releasing the longitudinal compressive stresses at the longitudinal ends of the inner element and allowing the inner and outer elements to relax inwardly, such that a tendency toward a greater degree of relaxation strain in the outer element will cause the outer element to grasp firmly the exterior of the inner element. The compound billet formed by this technique may thereafter be extruded through a suitable die aperture so as to produce an elongated, compound product, e.g., a copper-clad aluminum wire or busbar.