Effects of extrusion speeds on grains environment of magnesium by combined extrusion

Abstract

In this paper, 3D computational models of extrusion-shear process of AZ31 magnesium alloy by compound extrusion die with different extrusion speeds have been studied. Simulations results are utilized to predict the evolutions of extrusion forces, temperatures and microstructures of magnesium alloy in rods. Coupled thermo-mechanical FEM model of extrusion process incorporating the material properties and simulation conditions (initial and boundary) have been applied. Theories of heat generation during extrusion have been discussed. A series of extrusion-shearing experiments and microstructure observations have been done to perform tests in order to validate the FEM simulation results with different ram speeds. The effects of ram speeds on the temperature distribution and extrusion environment have been researched. The temperature developed in extrusion increases with increase of ram speeds. Temperature rise is due to the fact that the strain rate is directly proportional to the ram speed, and the magnitude of the generated heat is proportional to the strain rate. Increasing the ram speed would produce a tendency to increase the extrusion forces. The strain rates caused by ES die increase with rise of ram speeds. The average grains size for magnesium alloy prepared by extrusion-shear decrease with the rise of ram speeds. The results of these simulations and experiments help to understand the mechanisms of extrusion-shear technology and assist in improving quality of wrought magnesium alloys.