Strain variation during bimetallic PM preform tube extrusion

Abstract

It is usually assumed that during plastic deformation of bimetals, the components must undergo an identical deformation for a sound metal forming operation. However, differences in microstructures and properties between simultaneously deformed metals make the flow heterogeneous. The present paper examines the variation in strain of each metal during extrusion of bimetallic tubes and transition joining between dissimilar PM preforms. It is shown that consolidation and metal matrix hardening mechanisms associated with PM preform deformation strongly affect the deformation behaviour of each metal and the onset of steady state deformation during extrusion.The results indicate that, during extrusion of PM bimetallic tubes, the difference in strain between core and sleeve is relatively small. The strain difference (between two metals) increases with increasing total strain, hard-core or low volume ratio during extrusion. In the case of transition joining of dissimilar PM preforms, softer metal experiences lower strain owing to triaxial constraints imposed by the tools and bottom hard metal.