Macroscopic Constitutive Model Of Magnesium Alloys Based On Meso Deformation Characteristics And Numerical Simulation

Magnesium and magnesium alloy materials,as a kind of light metal materials,make it more attractive for the lightweight design of automobile,aircraft and other vehicles.Due to the HCP crystal structure,the deformation capacity of magnesium alloys at room temperature is limited.The plastic behavior and texture evolution of magnesium alloys under different loading conditions were studied by experimental observation,theoretical modeling and numerical simulation.The main contents of this paper are as follows:1.In order to study the plastic behavior of magnesium alloy,the uniaxial tensile test,uniaxial compressive test,uniaxial cyclic test and metallographic test were carried out with AZ31 magnesium alloy extruded bar,and the plastic behavior differences of materials under different loading modes were analyzed.When uniaxial tension was carried out along the extrusion direction of magnesium alloy bar,the stress-strain curve of the material present a"convex"shape,and the plastic hardening rate first gradually increase and then decrease,finally tend to saturation.When uniaxial compression was carried out along the extrusion direction of magnesium alloy bar,the stress-strain curve of the material present an"S"shape.The plastic hardening rate first increase slowly and then rise rapidly,finally tend to saturation.When the magnesium alloy bar was reverse stretched after compression along the extrusion direction,the stress-strain curve of the material also presents an"S"shape.Based on observation and comparison of the microstructure of the undeformed material and the deformed material,it was found that there are almost no twins in the microstructure of the material after uniaxial tensilion and cyclic deformation.However,there are a large number of twins after uniaxial compression,indicating that the difference in mesodeformation mode is the cause of the difference in the macroscopic plastic behavior of magnesium alloy material.2.In order to establish macroscopic constitutive model which can effectively describe the complex plastic behaviors of magnesium alloys,based on characteristics of the slip,twinning and untwining mesoscopic deformation modes,respectively set up three corresponding function of the yield surface radius evolution,using Mises yield criterion,and developed a magnesium alloy macro plastic constitutive model that includes three morphing modes.Considering the effect of crystal orientation on material mechanics behavior,by giving each unit an initial orientation,the deformation mode of occurrence and crystal orientation were associated.In order to describe crystal orientation rotation caused by twinning deformation,a new method for calculating grain reorientation was presented by using Rodrigues rotation formula.And introducing temperature correlation to this model so that the constitutive model can describe the plastic behavior in a certain temperature range.In this paper,the implicit integral algorithm and the uniform tangent stiffness matrix of the constitutive model were derived.On this basis,the ABAQUS material user subroutine is written to realize the finite element calculation of the constitutive model.Combined with the experimental data,the numerical simulation of the plastic behavior of magnesium alloys under uniaxial tensile,uniaxial compressive and cyclic loading were carried out by using the single element model.The simulation results show that the macroscopic hardening behavior of magnesium alloys under three loading conditions is consistent with the experimental results.3.The extrusion and rolling process of magnesium alloy with random texture were simulated by volume representative element.The results show that the deformation is non-uniform in both cases.Using solid model to simulate the rolling forming process of magnesium alloy,analyzed stress and strain distribution of magnesium alloy sheet and the texture evolution under different condition that were strain rate of 0.1s^-1,the reduction of2%,5%and 8%respectively.The results show that when the reduction is 2%,the average residual stress and strain of the plate is the smallest,were 22.873 MPa and 1.77×10^-2;When the reduction is 8%,the average residual stress and strain of the plate is the largest,which is 36.41MPa and 8.736×10^-2,respectively.Considering the deformation capacity of magnesium alloy at room temperature and the production cost of rolling forming,5%reduction is suitable for cold rolling.When the rolling is finished,the material evolves from the initial random texture to the typical strong base texture,and The basal texture is more intense with the increase of the rolling reduction.