Cross flow during twist extrusion: Theory, experiment, and application

Upon intensive investigation during the recent years, severe plastic deformation (SPD) has been commonly accepted as a strong tool for improving mechanical properties of metallic materials. The interest in commercial use of SPD materials with superior properties addresses the issue of scaling up the SPD methods. In this regard, methods that can provide SPD conditions in billets with large dimensions become of prime interest. Twist extrusion (TE) is such a process, whereby large strains are accumulated owing to repeated extrusion through a die that imposes shearing stresses. Despite a few studies of TE in the literature, many features of the process's nature remain unclear or even unknown. In the current article, we have studied an important effect of TE named "cross flow" that previously received scarce attention. By performing both experiments and simulations, we elucidated the mechanism of the cross flow as well as how it is affected by material properties and process conditions. Since practical significance of the cross flow became apparent, special attention was paid to the problem of control and reliable prediction of the cross flow. Finally, prospective applications of the investigated effect were suggested. Conclusions of the current study are anticipated to contribute to further research on simulation of other simple-shear-based SPD processes.