Features of Twist Extrusion: Method, Structures & Material Properties

Abstract

During the last decade it has been shown that severe plastic deformation (SPD) is a very effective for obtaining ultra-fine grained (UFG) and nanostructured materials. The basic SPD methods are High Pressure Torsion (HPT) and Equal Channel Angular Extrusion (ECAE). Recently several new methods have been developed: 3D deformation, Accumulative Roll Bonding, Constrained Groove Pressing, Repetitive Corrugation and Straightening, Twist Extrusion (TE), etc. In this paper the twist extrusion method is analyzed in terms of SPD processing and the essential features from the “scientific” and “technological” viewpoint are compared with other SPD techniques. Results for commercial, 99.9 wt.% purity, copper processed by TE are reported to show the effectiveness of the method. UFG structure with an average grain size of ~0.3 μm was produced in Cu billets by TE processing. The mechanical properties in copper billets are near their saturation after two TE passes through a 60º die. Subsequent processing improves homogeneity and eliminates anisotropy. The homogeneity of strength for Cu after TE is lower than after ECAE by route BC, but higher than after ECAE by route C. The homogeneity in ductility characteristics was of almost of inverse character. The comparison of mechanical properties inhomogeneity in Cu after TE and ECAE suggests that alternate processing by ECAE and TE should give the most uniform properties.

Evolution of Microstructure and Hardness in Pure Al by Twist Extrusion

“…The twisting die has a twist line slope with an angle of ¼ 60 in the counter clockwise direction. With this geometry, average true strain of $1:2 4,5) is introduced for a single pass. As illustrated in Fig.…”

“…[1][2][3] Among many processing techniques available for SPD, twist extrusion (TE) is known as a promising SPD process. [3][4][5][6] However, TE has been less studied 7) and little is known for the evolution of microstructure and mechanical properties during TE process. Therefore, this study is initiated in order to conduct TE using pure Al.…”

Microstructure and Mechanical Properties of Copper Processed by Twist Extrusion with a Reduced Twist-Line Slope

“…[8] Rectangular bars for TE were machined from hot-rolled rods and then kept at 823 K (550°C, 0.5 T m ) for 1 hour. The samples that underwent only machining and heating are referred to as ''initial'' in this paper.…”

“…Twist extrusion (TE) was introduced [5] as an attempt to scale-up the process of high-pressure torsion. Being promising in the commercial sense, [6] TE enjoyed some interest, which is reflected in continuous research on the subject [7][8][9][10][11][12][13] as well as in the emergence of new SPD methods inspired by the concept of TE. [14][15][16][17][18] In the quest to incorporate TE into the industry, such issues as endurance of the tool are becoming important.…”

“…[5] With this relation, reducing the twist-line slope, b (by decreasing angle a or increasing length H), can be expected to increase the endurance of the TE die. For example, replacing TE dies having b = 55 to 60 deg, which are most commonly used at the laboratory scale, [7][8][9]20] by TE dies with b = 35 to 40 deg should double the fatigue life of the die according to Eq. [1].…”