Study on metal flow in extrusion billet is fundamental and useful to understand extrusion technology. In particular, knowing the behavior of skin of extrusion billet is indispensable to maintain qualities of extrusions. In order to investigate its behavior, extrusion experiments of clad billet and the FE analysis by DEFORM-2DTM were performed. The calculated behavior of billet skin was similar to that in experiment. It was considered that the results of FE analysis were acceptable to estimate the actual behavior of metal flow in extrusion. The billet skin penetrated the core in indirect extrusion and it was piled up at the back end of billet in direct extrusion. Slight dead metal zone appeared on the outer side of die face in indirect extrusion. Shear zone appeared between dead metal zone and flow zone in direct extrusion. Moreover, die semi-angle affected the behavior of billet skin in direct extrusion. 70 degree semi-angle die restrained billet skin from entering extruded product compared with 90 or 110 degree semi-angle die.
