Numerical Investigation of the Cross-section and Twist Extrusion Die Angle on the Distribution of Plastic Strain and Microstructure of Al7050 Alloy

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 effect 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 finite 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 effects 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 significantly 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 100ffm to 6ffm in a single pass and requires the lowest extrusion force.