The simulation researches on hot extrusion of super-fined tube made of magnesium alloys

Abstract

To research the deformation mechanisms of extrusion for artificial blood vessel. A series of experiments were done to obtain the simulation parameters: stress-strain curves, friction factors and heat transfer coefficient, etc. Three-dimensional, coupled thermo-mechanical finite element simulations of extruding a wrought magnesium alloy were performed. Computed parameters including workpiece material characteristics and process conditions (billet temperature, reduction ratio, and ram speed) were taken into consideration. The temperature distribution of the transient-state extrusion is different from the steady-state extrusion. There exists heat flow in two reverse directions. The maximum temperature is found to be at the center of small tube along the longitudinal direction, while the minimum temperature is found at the edge of the billet in contact with both the container and the die face. The material at the center of the profile has a lower strain rate and therefore it flows through the die with less severe deformation. It is clear that the metal flow velocity field along the negative Y axis remains steady during tube extrusion, so artificial blood vessel with homogeneous microstructures would be obtained. The maximum damage occurs at the billet surface in the exit region of the die. This is because critical damage occurs at the point of maximum tensile stress in the tube. The extrusion simulation was the reliable predictions of strain rate, effective strains, effective stresses and metal flow velocity in an AZ31 billet during direct extrusion.