Shaorui Zhang

Dynamic recrystallisation and dynamic precipitation in AA6061 aluminium alloy during hot deformation

Abstract Deformation behaviour of AA6061 alloy was investigated using uniaxial compression tests at temperatures from 400 to 500°C and strain rates from 0·01 to 1 s−1. Stress increases to a peak value, then decreases monotonically until reaching a steady state. The dependence of stress on temperature and strain rate was fitted to a sinh-Arrhenius equation and characterised by the Zener–Hollomon parameter with apparent activation energy of 208·3 kJ mol−1. Grain orientation spread analysis by electron backscattered diffraction indicated dynamic recovery and geometrical dynamic recrystallisation during hot compression. Deformation at a faster strain rate at a given temperature led to finer subgrains, resulting in higher strength. Dynamic precipitation took place concurrently and was strongly dependent on temperature. Precipitation of Q phase was found in the sample deformed at 400°C but none at 500°C. A larger volume fraction of precipitates was observed when samples were compressed at 400°C than at 500°C.

A Crystalline Plasticity Finite Element Method for Simulation of the Plastic Deformation of AZ31 Magnesium Alloys

In this paper, a constitutive framework based on a crystalline plasticity model is employed to simulate the plastic deformation of AZ31 magnesium alloy, which posses the hexagonal close packed (HCP) crystal structure. Dislocation slip and mechanical twinning are taken into account in the model. The successive integration method is used to determine the active slip systems, and the contribution of twinning to the grain reorientation is treated by the PTR method. The FE model is introduced into ABAQUS/Explicit through a user material subroutine (VUMAT). Three deformation processes of AZ31 magnesium alloy, including tension, compression and a stamping process, are simulated with the present method. The simulation results are compared with experiment and those presented in the literature.

Modeling texture evolution during rolling process of AZ31 magnesium alloy with elasto-plastic self consistent model

Abstract To gain a better understanding about texture evolution during rolling process of AZ31 alloy, polycrystalline plasticity model was implemented into the explicit FE package, ABAQUS/Explicit by writing a user subroutine VUMAT. For each individual grain in the polycrystalline aggregate, the rate dependent model was adopted to calculate the plastic shear strain increment in combination with the Voce hardening law to describe the hardening response, the lattice reorientation caused by slip and twinning were calculated separately due to their different mechanisms. The elasto-plastic self consistent (EPSC) model was employed to relate the response of individual grain to the response of the polycrystalline aggregate. Rolling processes of AZ31 sheet and as-cast AZ31 alloy were simulated respectively. The predicted texture distributions are in qualitative agreement with experimental results.

Simulation of texture evolution during plastic deformation of FCC, BCC and HCP structured crystals with crystal plasticity based finite element method

Two alternative formulations of single crystal plasticity model were introduced respectively and two schemes were implemented in the explicit FE code with software ABAQUS/Explicit by writing the user subroutine VUMAT. Meshes containing material data were created with solid elements. Each element represented an individual grain, and the grain orientations were explicitly stored and updated at each increment. Tangential modulus method was employed to calculate the plastic shear strain increment of deformation systems in combination with a hardening law to describe the hardening responses. Both two developed subroutines were applied to simulate the texture evolution during the uniaxial tension of copper (FCC), cold rolling of IF steel (BCC) and uniaxial compression of AZ31 magnesium alloy (HCP). The predicted texture distributions are in qualitative agreement with the experimental results.

Polycrystal modeling of hot extrusion texture of AZ80 magnesium alloy

Abstract The visco-plastic self-consistent (VPSC) model is extended to take the dynamical recrystallization (DRX) into account so that the hot extrusion texture of AZ80 magnesium alloy can be properly modeled. The effects of extrusion temperatures and imposed boundary conditions on the resulting textures were investigated, and good agreement can be found between the simulated and the measured extrusion textures. The simulated results show that the DRX grains are responsible for the formation of the fiber component since the poles of the DRX grains are tilted away from those of the unrecrystallized grains during the formation of their high angle boundaries (HABs). Furthermore, the basal poles of the grains are favorably oriented to the transversal direction (TD) where the imposed deformation is larger due to lower slip resistance of the basal slip. The elevated temperature enhances the activity of pyramidal «c+a» slip modes and gives rise to a larger recrystallized volume fraction, resulting in a weakened extrusion texture.

Forming limit diagram analysis based on crystal plasticity for magnesium alloy sheets

In the sheet metal forming industry, forming limit diagram (FLD) is a useful tool for quantifying metals formability. However, the experimental measurement of FLD is difficulty, time consuming and expensive process. It would be useful if FLD calculated with a theoretical model could replace experimental measurements. In this research, a rate independent crystal plasticity model is developed to analyze the plastic deformation of hexagonal close packed (HCP) materials by incorporating the crystallography of deformation twinning in plasticity model. The numerical simulations of FLD for AZ31 magnesium alloy are performed based on the crystal plasticity model incorporated within the Marciniak- Kuczynski (M-K) approach. The approach allows for the incorporation of initial texture, evolution of texture, and texture-induced anisotropy. The effects of mechanical twinning on plastic deformation and FLD behavior for AZ31 alloy are also incorporated. Finally, the calculation of the FLD for AZ31 alloy successfully pre...

Simulation of cylindrical cup drawing of AZ31 sheet metal with crystal plasticity finite element method

As a light-weight structural material, magnesium alloys show good potential in improving the fuel efficiency of vehicles and reducing CO2 emissions. However, it is well known that polycrystalline Mg alloys develop pronounced crystallographic texture and plastic anisotropy during rolling, which leads to earing phenomenon during deep drawing of the rolled sheets. It is vital to predict this phenomenon accurately for application of magnesium sheet metals. In the present study, a crystal plasticity model for AZ31 magnesium alloy that incorporates both slip and twinning is established. Then the crystal plasticity model is implemented in the commercial finite element software ABAQUS/Explicit through secondary development interface (VUMAT). Finally, the stamping process of a cylindrical cup is simulated using the developed crystal plasticity finite element model, and the predicting method is verified by comparing with experimental results from both earing profile and deformation texture.

Analysis of BCC Sheet Metal Forming by Polycrystalline Plasticity method

The macroscopic deformation behavior of sheet metals is related physically to the microscopic deformation mechanism. For BCC metal, there have three kinds of slip systems, and the rules of the active slip system still not clear. A program is developed based on the proposed crystalline plasticity dynamic explicit finite element model to simulate sheet metal stamping as well as predict texture evolution. A stable proportion factor has been given to the different slip system and introduced into the rate‐independent polycrystalline model. A proper factor has been found by the contrast between the simulation result and experiment data.

Numerical Simulation on Sheet Metal Forming with Rate‐independent Polycrystalline Plasticity FEM

It has long been found that, during deformation process, the crystal orientations would gradually rotate around some ideal orientations, and then would affect the later deformation properties of sheet metal. So it is very important to introduce texture model into metal forming processes. In this paper, a rate‐independent polycrystalline plasticity model is developed and introduced into dynamic explicit element method. Metal flow is assumed to occur by crystallographic slip on given slip systems within each crystal. Every integration point represents a single crystal. Then cup drawing of sheet metal is studied using crystalline plasticity finite element analysis. For the rolled aluminum sheet, which contains strong {001}〈110〉 texture, earing is formed at 45° direction after cup drawing. For the annealing aluminum sheet, due to the balance between two main textures, the flange earing tendency is not obvious. And for the soft steel sheet with a faintish orientation distribution, the flange earing tendency is...