Deformation Characteristics of Asymmetric Gradient Extrusion in Preparing Ultra-Fine-Grained Bulk Materials

In this paper, a novel method for the preparation of ultra-fine-grained bulk materials called asymmetric gradient extrusion (AGE) is proposed. In AGE, the cross-section of the extrusion channel is a rectangle, and two inclined planes are staggered along the extrusion direction. To realize repetitive extrusion, the thickness of the workpiece is limited to be equal to the width of the channel outlet. In order to study the mechanism of ultra-fine grain formation in AGE, the deformation characteristics of AGE were investigated. First, the slip line field method was used to theoretically analyze the deformation characteristics and grain splitting in AGE. Then, the plastic deformation behavior of bulk samples in AGE and traditional extrusion was investigated and compared with the finite element method. In addition, the deformation characteristic and microstructure variation of pure copper bulk samples in AGE were experimentally investigated. The results showed that the deformation characteristics of workpieces were highly related to the two inclined planes within the die channel. Two independent deformation zones can be formed with increasing distance between the two inclined planes. The shear effects in each deformation zone lead to grain splitting during extrusion. Compared with traditional extrusion, the advantage of AGE is its amazing ability to form high and uniform strain during extrusion, which leads to the formation of small and uniform grains in the workpiece. After six passes of AGE, an average grain size of 0.6 mu m can be achieved. The enhancement and accumulation of dislocations within grains was the dominating mechanism of grain fragmentation. AGE shows impressive potential in the preparation of ultra-fine-grained bulk materials.