Abstract
A new hot hydrostatic extrusion process with a visco-plastic pressure medium instead of liquid was developed. A lump of visco-plastic material is introduced into a container just after charging a pre-heated billet, and extrusion is immediately performed. Therefore, the temperature drop of billet is minimized, and at the same time a steady hot extrusion is realized.
With this process, co-extrusions of commercially pure titanium and copper alloy were conducted. And favourable extrusion conditions were determined for sound composite bars. For the co-extrusions of titanium and other materials, a heat-treated or axisymmetrically pre-deformed billet of titanium should be used to obtain an uniform deformation.
An intermetallic compound was sometimes observed at the interface between titanium and copper alloy when the extrusion temperature was high, or the annealing temperature after extrusion was high. Under a good process condition, no intermetallic compound was observed and the bonding shear strength was as high as 120-150MN/m2 for the case of a titanium clad copper electrode.
