Research On Anisotropic Behavior Of Extrusion Magnesium Alloy Based On Crystal Plasticity Theory

With the continuous advancement of society,the demand for resources is increasing.However,resources such as coal and petroleum are not renewable.Therefore,the development of new functional materials is one of the important ways of reducing energy consumption,reducing pollution and protecting the environment,and achieving sustainable development of people and nature,solving the problem of increasing global resources and deteriorating environment.Magnesium and magnesium alloys are the lowest density of metal materials used in practical engineering applications.They have high specific strength and specific stiffness,good dimensional stability,excellent seismic performance,good heat dissipation,good shielding performance and good recyclability.And other advantages,in the transportation industry,medical industry,electronics industry,communications and communications industry,aerospace and other fields have very broad application prospects.China's magnesium resource reserves rank first in the world.The development of magnesium alloy preparation and processing technology is of great significance to realize the transformation from magnesium resource advantage to economic advantage.The crystal structure of magnesium and its alloys is a close packed hexagonal(HCP)structure.The lattice constant of magnesium crystal is a=0.3209 nm,c=0.5211 nm,and the axial ratio c/a=1.624.The axial ratio and tightly packed spheres are obtained.The theoretical ratio is very close to 1.633.Due to the unique HCP structure of magnesium alloy,it has less independent slip system,low plastic deformation capacity at room temperature(average elongation of about 12%),poor plastic forming ability during processing and application.Due to the special close-packed hexagonal(HCP)structure of magnesium crystals,the symmetry is low,and the amount of active slip coefficient is insufficient during elastoplastic deformation,resulting in strong plastic anisotropy and tensile and compression asymmetry of magnesium and magnesium alloys.This anisotropy and the asymmetry of tension and compression cause the plastic deformation process ofmagnesium alloy to be more complicated,which affects the application range of magnesium alloy.In this paper,the anisotropy behavior of magnesium alloys is studied based on crystal plasticity theory.The main work is as follows:(1)After pre-stretching of extruded AZ31 magnesium alloy bars in different axial directions(ED),the torsion test was carried out,and the microstructure observation experiment was carried out to study the axial pre-tension loading on the extrusion.The influence of torsional deformation of AZ31 magnesium alloy bar,the influence of axial pre-tension loading on the deformation mechanism of torsional deformation is explored;(2)The extrusion of AZ31 magnesium alloy bar is carried out in different directions along the extrusion(ED)direction.Pre-compression,torsion deformation test after unloading,and related microstructure observation experiments,to study the effect of axial pre-compression loading on torsional deformation of extruded AZ31 magnesium alloy bar,and explore the axial pre-tension loading to torsional deformation(3)Establish a viscoplastic self-consistent model,simulate the effects of the above two preloadings,and analyze the influence of pre-deformation on the anisotropic behavior of AZ31 magnesium alloy.