Analysis of double maximum flow patterns in axisymmetric extrusion of H30 aluminium alloy

Abstract

Unusualflow patterns, where two maxima occur symmetrically about the extrusion axis separated by a minimum at the axis, were obtained in the axisymmetric hot extrusion of an aluminium alloy. Hot torsion tests were used to determine the hot deformation characteristics of the alloy and a modified visioplasticity technique was used to obtain quantitative values of strain rate, strain, temperature rise, and flow stress in the deformation zone. It is concluded that the double maximum flow patterns are caused by the combined effects of the negative strain-hardening coefficient of the material and the extrusion conditions. Increasing the friction, increasing the extrusion speed, and decreasing the die angle enhanced the double maximum flow.