| In this thesis commercial AZ31magnesium alloy in the forms of extruded bar witha strong fiber texture and hot rolled plate with a strong basal texture was chosen as thestarting material. In total, seven kinds of specimens for compression were prepared.Two types of specimens were cut from extruded bar with their compression axis alignedperpendicular or parallel to the extruded direction. The other five types of specimenswere cut form hot rolled plate with their compression axis aligned0o,30o,45o,60oor90oto the normal direction （ND） of the rolled sheet, respectively. Uniaxial compression,plane strain compression and dynamic plastic deformation （DPD） had been carried outat different temperatures and strain rates. The microstructure and texture evolutionduring deformation had been quantitatively characterized using electron backscatterdiffraction （EBSD）. The EBSD data had also been applied to analyze in detail theinfluence of initial orientation and deformation conditions on yield behavior, workhardening behavior and dynamic recrystallization （DRX） of AZ31during compression,and thereby to understand the relationship between mechanical properties andmicrostructure better.Main conclusions found are as following:①The CRSSs for slip and twinning systems in AZ31magnesium alloy areestimated via an advanced Taylor model. A reconstruction mapping methods forenhancing the EBSD map contrast has been developed in order to reveal strong grainsubdivision behavior.②The effect of initial texture on stress-strain behavior is strongly dependent ontemperature. At low temperature, the mechanical behavior is highly anisotropicoriginated from the initial texture, which affects the activation of twinning and slip.With increasing temperature （above250℃）, the twinning activity decreasessignificantly, thus the mechanical behaviors become more isotropic due to the operationof a larger number of slip modes. The activation energy for0o,30o,45o,60oand90ospecimen is146.71KJ/mol,141.88KJ/mol,127.56KJ/mol,137.62KJ/mol and151.37KJ/mol, respectively. The activation energy of45ospecimen is the lowest due to itsinitial texture is favorable for basal slip.③Initial texture has a significant influence on the macroscopic morphology ofdeformed specimens. The macroscopic morphology of specimens compressed at different temperatures and strain rates are highly anisotropic. The shape of thecompression face of deformed specimens varies with initial texture in the form ofellipse. The order of the ratio of long axis to short axis is0°<30°<90°<45°<60°.④Initial texture has an important effect on yield stress and strain hardeningbehavior. Compressive stress-strain behavior is highly anisotropic with respect to theinitial texture at room temperature. The significant yield behavior can be observed ifonly a small volume of twins are activated. The increasing strain hardening rate（corresponding to the stage II） is mainly caused by texture strengthening, which rotatesgrain orientations into hard orientations due to {10（?）2} twinning. The length of the stageII is determined by the volume fraction of grains which are favorable for {10（?）2}twinning.⑤{10（?）2} twinning variant selection mechanism can be explained by the Schmidfactor （SF） statistically. In general twinning variants with the highest SF are mostfrequently observed, however the SF alone cannot explain all the twinning activated.⑥Twinning activities of0oand90ospecimens are largely enhanced by DPD.Several twinning modes including {10（?）1},{10（?）2} and {10（?）1}-{10（?）2} are observed in0ospecimen. The {10（?）1}-{10（?）2} double twinning behavior exhibits strong orientationdependence because of its high CRSS, while {10（?）2} twinning occurs over a wide rangeof Schmid factor from0.05to0.5. For the90ospecimen,{10（?）2} twinning is dominantunder both DPD and quasi-static conditions, and the {10（?）2} twinning variant selectionmechanism is governed by the Schmid factor criterion, which is insensitive to strain rate.However, strain rate could significantly affect the competition between twin nucleationand twin growth. Twin nucleation will be largely enhanced by DPD while twin growthwill be favored under quasi-static loading.⑦The DRX process is closely related to initial texture. The DRX process in90ospecimen is significantly retarded compared with that in0ospecimen compressed at350℃. The difference of DRX process between0oand90ospecimens is attributed todifferent deformation mechanisms at the starting deformation stage. With respect to0ospecimen, pyramidal <c+a> slip is considered as the main deformation mechanism. For90ospecimen, prismatic <a> slip is the dominant deformation mechanism.⑧The effect of strain rate on DRX behavior is caused by its influence on the slipand twinning deformation mechanisms. For the0ospecimen compressed at250℃,continuous DRX, discontinuous DRX and rotation DRX are mainly observed at thestrain rate ranging from0.001to0.01s-1, while rotation DRX and twinning induced DRX are mainly observed at the strain rate of1s-1, and {10（?）1}-{10（?）2} double twinninginduced DRX is mainly observed at the strain rate of5s-1.⑨Grain subdivision behavior which corresponds of course to different slipsystem activity/combinations in different parts of each grain is observed. The deformedbands are nearly perpendicular to the （0001） basal plane. However, there is no directrelationship between the bands and the loading direction. The DRX would be enhanceddue to the grain splitting by the deformation bands. |
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