Use of powder metallurgy preforms as alternative to produce bimetallic tubes

Coextrusion is one of the major processes used to produce bimetallic rods, tubes and wires. Previous investigations into the coextrusion of wrought metals have shown that, for the production of a sound coextrusion, the available processing zone is very narrow, with little flexibility in terms of tool and process parameter selection. These limits have many practical implications in the selection of suitable material and process parameter combinations. The present investigation envisages the production of sound bimetallic tubes by controlling the initial materials characteristics through the powder metallurgy (PM) and cold extrusion route. It is shown that the consolidation of PM preforms during extrusion reduces the differential velocity between the core and the sleeve, and high friction at the interface aids sound flow over a wide range of processing conditions. In addition, the non-uniformities of deformation (especially on the hard metal side) are accommodated by the softer preform near the interface, through micromechanical interaction. The present approach implies manufacturing flexibility and reduction of tool/ amortisation costs for the production of bimetals. © 2005 Institute of Materials, Minerals and Mining.