Simulation And Parameter Analysis Onthe Plastic Deformation Behavior Of AZ31magnesium Alloy

Due to its low density and large reserve on earth, magnesium becomes one of the most promising engineering materials. However, magnesium has a poor ability of plastic deformation at room temperature which is mainly cause by its crystal structure and limited slip systems that could be activated at RT. In order to improve its plasticity at RT many researchers have been working on it. The aim of the thesis is to combine experimental data and VPSC model to simulate the plastic deformation behavior of Mg.In this study, we studied the mechanical behavior of AZ31 rolled plate when compressed and pulled in different directions. To obtain different deformation mechanisms, samples were deformed in different paths, then we analysis how the material's parameters affect the plastic deformation. In the experiment, samples were deformed to different strain in two directions, namely TD and ND. The results were predicted using VPSC model combined with optical microscope, X-ray diffraction and electron back scattering diffraction(EBSD).The results show:1) {10-12}twining appears at the beginning of plastic deformation, and these twins consume and reorient the favorably oriented grains. 2) when strain reaches 0.05-0.06 {1011} twinning starts to be a deformation mechanism. The number of compression twins growss with increasing strain until rupture. 3) In compression, a total strain higher than 0.15 is accommodated when compression twinning is an important deformation mechanism. So, despite the strain localization within the compression twins, quite a lot of deformation can be accommodated before rupture. 4) Modeling with the VPSC can accurately predict the flow stress during large plastic deformation, as well as the twinning activity, the evolution of volume fractions of twins and the overall texture evolution. 5) In simulations, twinning does not generate extra hardening and slip does not need a higher latent hardening parameter from twin activity. In many other publications, slip needs a higher latent hardening parameter from extension twinning to fit the stress-strain curves. 6) At high strain, although the fractions of compression twins are similar, the experimental and simulated flow stress during ND compression is lower than that during TD compression. At the same time, we deformed the samples in four different paths: compression along normal direction(TTC), compression along rolling direction(IPC), compression at 45 o between normal direction and rolling direction, tension along transverse direction. How material parameters affects deformation behavior predictions. The conclusions are: 1) An accurate determination of the threshold stresses?sinvolves at least four deformation paths, each one favoring one of the deformation mechanisms. Experiments must include both tension and compression tests. 2) The simulated flow stress strongly depends on the highest threshold stress?s among the activated modes, whereas variation of the threshold stress for basal slip produces small flow stress change. 3) The strain anisotropy(r-values)is more parameter-dependent in tension than in compression. Thus measurement of the r-value in tension can be used to determine the relative threshold stresses. 4) Simulated {10-12} twin volume fraction depends more on the model and texture than on the parameters, at least with reasonable CRSS for Mg alloys. 5) It has been possible to simulate the flow stress with latent hardening moduli for slip hss' =1, but {10-12} twinning clearly generate an extra hardening hst>1. 6) When the sample of prestrained 3% deformed to 1%, 2%, 2.5%, the intensity of the texture along RD decreases, while the intensity of the texture along TD increases, which indicates that there could be detwinning behavior accompanied with dislocation activity that rotates the gain.