Plastic flow of aluminium extruded under complex conditions

Abstract

This paper describes the extrusion process of aluminium in which cyclic changes of the strain path are induced in the natural deformation zone of the extruded piece of metal, through reversible rotation of the die (patented KOBO metal forming process). Such a procedure allows significant reduction in the extrusion force, as well as in the global mechanical work needed for the extrusion of a rod when compared with the conventional process. Macro- and microstructural observations of the products and microhardness and tensile tests show that cyclic changes in the strain path cause a reduction in the differences in the rate of plastic flow in the particular microvolumes of the metal, and lead to structural homogenisation. This process also causes a significant improvement in the plasticity of the extruded rod and a reduction in its work hardening.