The effect of the die rotation during extrusion on the shape of embedded markers

Abstract

The introduction of die rotation during extrusion changes the material flow pattern. An initially straight flow marker embedded into a billet to visualise plastic flow is twisted into a spiral during rotation-assisted extrusion in addition to the reduction in the cross-sectional area. Moreover, the shape of the marker as observed on two-dimensional sections perpendicular to the extrusion axis changes from a circle to a teardrop. A simple model was proposed to describe these changes. The method is based on two transformations to account for the grid pattern distortion during conventional extrusion without rotation and for the torsion due to the die rotation. A good agreement was obtained between calculations and experimentally observed marker shape changes during high-pressure torsion extrusion and previously reported results for friction stir extrusion.