Influence of Outer Corner Radius in Equal Channel Angular Pressing

Equal Channel Angular Pressing (ECAP) is currently being widely investigated because of its potential to produce ultrafine grained microstructures in metals and alloys. A sound knowledge of the plastic deformation and strain distribution is necessary for understanding the relationships between strain inhomogeneity and die geometry. Considerable research has been reported on finite element analysis of this process, assuming threedimensional plane strain condition. However, the two-dimensional models are not suitable due to the geometry of the dies, especially in cylindrical ones. In the present work, three-dimensional simulation of ECAP process was carried out for six outer corner radii (sharp to 10 mm in steps of 2 mm), with channel angle 105 , for strain hardening aluminium alloy (AA 6101) using ABAQUS/Standard software. Strain inhomogeneity is presented and discussed for all cases. Pattern of strain variation along selected radial lines in the body of the workpiece is presented. It is found from the results that the outer corner has a significant influence on the strain distribution in the body of work-piece. Based on inhomogeneity and average strain criteria, there is an optimum outer corner radius. Analysis, strain inhomogeneity, plastic equivalent strain, ultra fine LTRA-FINE grained materials have been widely investigated due to their improved mechanical properties such as high strength and ductility. Various techniques have been developed to obtain such mechanical properties. Among these, the Equal Channel Angular Pressing (ECAP), originally developed by V. M. Segal [1-2], is one of the effective methods of obtaining materials with high strength and toughness. In ECAP, a work-piece is pressed through a die that contains two channels with equal cross-section meeting at an angle 2 , having corner angle and outer corner radius R as shown in Fig. 1. Since the cross-section of the workpiece remains unchanged, the process can be repeated until the accumulated deformation reaches a desired level. High strain can be achieved with multiple passes due to its cumulative nature. In multiple pass, different routes may be employed; Route A: in which the orientation of work-piece remains unchanged in successive passes; Route B: in which the workpiece is rotated by 90° about its longitudinal axis; Route C: in which the work-piece is rotated by 180° about its longitudinal axis. 1 Ph.D.; Department of Industrial & Production Engineering, BVB College of Engineering & Technology, Hubli-580031 (India); ; Phone: 00919379662424 2 Ph.D.; Department of Metallurgical & Materials Engineering, Indian Institute of Technology – Madras, Chennai-600036 (India). The work-piece under extrusion can be divided into four zones namely (a) head (the front of the work-piece), (b) body, (c) plastic deformation zone and (d) tail (the undeformed portion at the end of the work-piece) as shown in Fig. 2. It is important to know the effect of geometry on the distribution of strain in these zones. The strain per pass can be calculated by the equation (developed by Iwahashi [3]) 2 cos 2 cot 2 3 1 ec p where p is the equivalent plastic strain (termed as ‘strain’ for convenience in this paper), 2 is the channel angle and is the corner angle as shown in Fig. 1. It is a closed equation with two parameters ( and 2 ), that predicts p for a given die geometry. The strain obtained from the equation does not give details of strain variation across the cross section of the work-piece. The distribution of strain is greatly influenced by the outer corner radius and this can be obtained by Finite Element Method.