Development of a co-extrusion press for the aluminum stabilization of NbTi superconducting wire.

It has long been recognized that high purity aluminum offers several potential advantages in the stabilization of superconductors. Previous attempts to fabricate commercially viable aluminum stabilized conductors have, however, been unsuccessful because of the great disparity in the metal forming properties of NbTi and aluminum. This disparity of flow stresses has led to the use of higher resistivity aluminum alloys as conductor matrices. These conductors have met with marginal success. The present approach involves applying aluminum to a NbTi/copper composite. The challenge is, of course, achieving complete metallurgical bonding and uniform cross-section. Through the use of an orthogonal extrusion process whereby aluminum is solid state bonded to a copper conductor we have successfully clad a wide range of superconductors with high purity aluminum. our latest effort culminated in cladding two pieces of 30,0001 of NbTi wire having a 0.5mm cross- section and an aluminum/superconductor ratio of 3 to 1. Our current machine has a few shortcomings including: limited extrusion pressure, is sequential as opposed to continuous, aluminum chamber capacity, bonding irregularities. We feel these limitations can be overcome with the design of a larger machine incorporating proprietary modifications.