Finite-element modeling of nonisothermal equal-channel angular extrusion

Abstract

Deformation during conventional (nonisothermal) hot working of metals via equal-channel angular extrusion (ECAE)was investigated using two-dimensional (2-D) and three-dimensional (3-D) finiteelement modeling (FEM) analysis. The effects of material flow properties, die-workpiece heat-transfer and friction conditions, and die design on metal flow were examined. Friction and die design were shown to be the most important parameters governing the formation of dead-metal zones during extrusion. On the other hand, thermal gradients induced by die chill and deformation heating were found to exacerbate the extent of flow localization that arises due to material-flow softening alone. The FEM predictions were validated by ECAE experiments on a Ti-6Al-4V alloy with a colony alpha microstructure. Preforms exhibited minor edge cracking and mild flow localization during extrusion at 985 ЊC, but severe shear localization and fracture during extrusion at 900 ЊC. The 2-D FEM simulations predicted deformation detail, including shear localization, that was in good agreement with the experimental results, but 3-D FEM simulations were required to realistically predict die chill. A combined approach, in which thermal data were extracted from 3-D simulations and inserted into 2-D simulations, produced load-stroke and fracture predictions in general agreement with measured values.

Developing Processing Routes for the Equal-Channel Angular Pressing of Age-Hardenable Aluminum Alloys

“…[31][32][33][34] However, an increase in temperature generally leads to grain growth, [35] and in age-hardenable alloys these higher temperatures may affect the size and distribution of the precipitates and thereby they may have a deleterious effect on the strength of the as-processed alloy. Accordingly, the present investigation was initiated with the objective of developing a processing routine that may be employed to successfully process various Al-ZnMg-(Cu) alloys by ECAP at room temperature.…”

Overview and Outlook for Materials Processed by Severe Plastic Deformation

“…The fmite-elementmodeling (FEM) work of Prangnell, et at. [30] and DeLo and Semiatin [31] provided further insight into the effect of die-geometry and friction on metal flow. DeLo and Semiatin also modeled ECAE under nonisothermal conditions.…”

The role of modeling in the development of advanced processes for metallic aerospace alloys

“…Flow localization may also be exacerbated when ECAE is conducted at elevated temperatures under nonisothermal conditions (i.e., using unheated tooling), as is common for high-temperature aerospace alloys. In these cases, FEM has proven to be useful in delineating the additional non-unifor mity in metal flow associated with heat-transfer for materials which also flow soften [49].…”