The effect of material properties and tooling design on deformation and fracture during equal channel angular extrusion Original Research Article

The effects of material constitutive behavior, tooling design, and friction conditions on metal flow, stress fields, and the tendency for tensile fracture during equal channel angular extrusion (ECAE) were established using a finite element modeling (FEM) technique. Three different material behaviors, typical of those encountered during cold and hot working, were investigated; these comprised (i) strain hardening, (ii) rigid, perfectly plastic, and (iii) flow softening types of behavior. The tooling geometries consisted of a so-called “simple” design with no moving channel members and a “complex” design with a sliding bottom floor. The FEM results indicated that the most uniform flow was obtained during ECAE of a strain-hardening material having a low strain-rate sensitivity in tooling with a sharp inner corner (“front leg”) radius. The ECAE of materials with other constitutive behaviors or in tooling with a radiused front leg showed some degree of flow nonuniformity, even away from the head and tail of the extrusion. Tooling design and material properties were also predicted to have an important influence on the tensile stresses and hence tensile damage developed during ECAE. The FEM results were validated using visioplasticity and fracture observations for AISI 4340 steel and a near-gamma titanium aluminide alloy.