Plastic deformation analysis of metals during equal channel angular pressing

Abstract

Severe plastic deformation (SPD) methods have been the subject of intensive investigation in recent years not only due to the superior physical and mechanical properties inherent to various ultrafine-grained materials, but also to several advantages of severely plastic-deformed materials compared to nano-structured materials manufactured by other methods through powder forms. Among various severe plastic deformation methods, equal channel angular pressing (ECAP), which involves a large simple shear plastic deformation by moving a workpiece through two intersecting channels has been the subject of intensive study due to its capability of producing fully dense samples containing ultrafine grain size. In this process, knowledge of the plastic deformation behaviour of the workpiece during the process is very important for the determination of the optimum process conditions such as die design, speed, temperature, friction and preform design. In this study, the rigid–plastic two-dimensional finite element method using the DEFORM2D code is presented for the better understanding of the plastic deformation behaviour of the workpiece. The material flow stress is considered to be the strain rate and strain dependant. The deformation within the workpiece is inhomogeneous unlike the ideal pure shear deformation. The pressed workpiece is divided into three zones (front, steady and end zones). It was also found that a lesser shear deformation zone occurs in the outer part of the workpiece, which is attributed to the faster flow of the outer part compared to the inner part within the main deformation zone. In particular, inhomogeneous deformation of the workpiece with respect to the effect of the friction factor is investigated.