Scale Effect in FEM Simulation of Axisymmetric Hot Micro-Extrusion of Aluminum Alloys

Hot micro-extrusion is a good candidate for manufacturing metallic micro-components with complex shapes and good mechanical properties. This work investigates the metal flow in direct hot mini- and micro-extrusion of aluminum rods by means of FEM simulations. The presented study was performed with the numerical code DEFORM 2D in axisymmetric mode using experimental material flow curves for AA 7108 alloy. The mini-to-micro dimensional scale factor was 10:1, the extrusion ratios were 16 and 100, and the ram speed ranged from 0.5 to 20 mm/s. The initial temperature of the billet and tooling was 400°C. It was found that the temperature distribution within the profile changed from mini-to micro-extrusion and the effect was more significant for higher reductions and higher extrusion velocities. The micro-scale effect increased the stress field just behind the die orifice and the material deformed more intensely to achieve the equilibrium velocity. It was shown that the scale effect can be evaluated by the relative strain rates associated with the corresponding deformation. Numerical results indicate that the scale effect does increase exponentially with the velocity and it becomes significant for final exit velocities of the extrudate above the level of 100 mm/s.