Journal of Stress Analysis Vol. 4, No. 2, Autumn - Winter 2019-20 Numerical Investigation of the Cross-section and Twist Extrusion Die Angle on the Distribution of Plastic Strain and Microstructure of Al7050 Alloy F. Heydari, H. Saljoghi, S.H. Nourbakhsh * Mechanical Engineering Department, Shahrekord University, Shahrekord, Iran. Article info Article history: Received 31 August 2019 Received in revised form 01 November 2019 Accepted 30 December 2019 Keywords: Twist extrusion Die angle Cross-section Severe plastic deformation Microstructure Abstract Twist extrusion is a novel method for severe plastic deformation of materials. Severe plastic deformation in metals creates small and uniform grain size and therefore increases their mechanical strength. In this study, the efect of die angle in twist extrusion and cross-section of extruded parts on plastic properties and microstructures of Aluminum 7050 alloy was investigated using DEFORM 3D fnite element software. Samples were simulated using dies with die angles of 20, 37, and 56 degrees with square, rounded-rectangular, and elliptical cross-sections. The aspect ratios of rectangular and elliptical cross-sections were also changed while keeping the cross-section area constant in order to investigate the efects of dimensions. Plastic strain distribution, gain size distribution, and the force needed for extrusion were extracted under all conditions. The results indicate that increase in die angle signifcantly reduces grain size and increases the force necessary for extrusion. Removing sharp corners in cross-section also results in more uniform plastic strain distribution and reduction in extrusion force. The elliptical cross-section with dimensions of 9×6mm which had the lowest dimension ratio can reduce grain size from 100฀m to 6฀m in a single pass and requires the lowest extrusion force. Nomenclature X Twist angle Q Activation energy L Length R Universal gas constant β Die angle T Absolute temperature σ p Peak stress X Dynamic recrystalisation fraction ˙ ε Strain rate ε 0.5 Strain for 50% recrystallization d 0 Initial grain size 1. Introduction Severe plastic deformations have been accepted in re- cent years as strong methods for improving the me- chanical properties of metal parts. Using these pro- cesses, it is possible to create microstructures with ul- trafne grains or even nanosized grains. These fne- grain materials can have higher strength and elonga- tion [1]. Examples of severe plastic deformation include ECAP [2], Twist extrusion [3], Friction stir process [4], ARB [5], HPT [6], etc. Twist extrusion is one of the most common methods for creating severe plastic de- * Corresponding author: S.H. Nourbakhsh (Assistant Professor) E-mail address: nourbakhsh.sh@eng.sku.ac.ir http://dx.doi.org/10.22084/jrstan.2019.19974.1106 ISSN: 2588-2597 1