Mesoscale Modeling and Validation of Texture Evolution during Asymmetric Rolling and Static Recrystallization of Magnesium Alloy AZ31B (original) (raw)
Related papers
2012
The focus of the present research is to develop an integrated deformation and recrystallization model for magnesium alloys at the microstructural length scale. It is known that in magnesium alloys nucleation of recrystallized grains occurs at various microstructural inhomogeneities such as twins and localized deformation bands. However, models need to be developed that can predict the evolution of the grain structure and texture developed during recrystallization and grain growth, especially when the deformation process follows a complicated deformation path such as in asymmetric rolling. The deformation model is based on a crystal plasticity approach implemented at the length scale of the microstructure that includes deformation mechanisms based on dislocation slip and twinning. The recrystallization simulation is based on a Monte Carlo technique that operates on the output of the deformation simulations. The nucleation criterion during recrystallization is based on the local stored energy, and the Monte Carlo technique is used to simulate the growth of the nuclei resulting from local stored energy differences and curvature. The model predictions are compared with experimental data obtained through electron backscatter analysis and neutron diffraction.
Microstructural evolution during recrystallization of magnesium alloys
2012
Microstructural evolution during the annealing of cold rolled Mg, Mg-1.5Nd and Mg-3Y sheets has been examined. The experimental results show a significant difference in recrystallization kinetics and grain growth between pure Mg and Mg-RE alloy sheets. Pure Mg sheet shows rapid recrystallization and grain growth, whereas recrystallization is considerably retarded in the Mg-RE alloys. Although recrystallized grains which are triggered at shear bands in the cold rolled pure Mg sheet show a relatively weak texture with a basal pole split into the sheet rolling direction, rapid grain growth is accompanied by re-strengthening of the basal-type texture. In contrast, a weak texture appears in the early recrystallization stage in Mg-RE alloys and is retained during annealing due to retarded recrystallization and grain growth.
Texture evolution during dynamic recrystallization in a magnesium alloy at 450°C
Acta Materialia, 2014
During thermomechanical processing of wrought magnesium alloys, the microstructure and texture continue to evolve as dynamic recrystallization (DRX) proceeds. New grains generated by DRX with a low dislocation density also participate in the texture evolution as the strain increases. However, the controlling mechanisms that drive the evolution are not yet understood. In this work, we studied texture evolution in an extruded Mg-Al-Mn alloy (AM30) during uniaxial compression at 450°C and under various strain rates ð_ e < 1:0 s À1 Þ. The tests were performed along the extrusion direction (ED) and the radial direction (RaD), respectively. Texture evolution was examined by electron backscatter diffraction and X-ray diffraction at different strains. At _ e < 0:1 s À1 , the effect of twinning was negligible. At _ e ¼ 0:5 s À1 , a high volume fraction of twins were activated but the twins were consumed by DRX as the strain increased. At _ e ¼ 0:8 s À1 , twins were not completely consumed by DRX, and the remaining twins had highly incoherent twin boundaries and contributed to the texture. In compression along the ED and with strain rates of 60.5 s À1 , prismatic slip dominated the texture evolution, and the final orientations clustered around h1 0 1 0ik ED and h2 1 1 0i || ED, resulting in two stable orientations with a 30°misorientation. At 0.8 s À1 , basal and pyramidal slip began to dominate the texture evolution at larger strain. In compression along the RaD, basal and pyramidal slip dominated the texture evolution, creating a texture located near h1 0 1 2i-h1 0 1 5i-h2 1 1 9i-h2 1 1 5i and h1 0 1 0i-h2 1 1 0i in the inverse pole figure. Texture simulations based on the Sachs and the viscoplastic self-consistent models show a satisfactory correlation between texture evolution and deformation modes.
Why do Magnesium Alloys Develop Sharp Textures Upon Dynamic Recrystallization?
Manuel/Magnesium, 2015
Using molecular dynamics (MD) simulations, we show that the maintenance of strong deformation texture during dynamic recrystallization of magnesium deformed at high temperature is controlled by the existence of energy landscape cusps and mobility spikes associated with specific grain boundaries generated by active deformation modes during the polygonization process. As the subgrains rotate to a final recrystallized state, they settle at misorientations with particular tilt axes that give out a best combination between low energy and high mobility of the associated grain boundary. Having identified the grain boundary types induced by extrusion of a commercial Mg alloy, AM30, we reconstructed them by MD simulations (notably of pure Mg) to identify their intrinsic defect structure via interfacial defect theory. These analyses enabled formal understanding of their excess potential energy variation with misorientation angles and their associated mobility. It is hypothesized that the change in the energy landscape and intrinsic defect structure induced by RE element additions, which highly segregate to the GBs, permits the subgrains to settle at more diverse misorientation angles, thus causing a weakening in the final texture.
Acta Materialia, 2009
Asymmetric rolling of commercially pure magnesium was carried out at three different temperatures: room temperature, 200°C and 350°C. Systematic analysis of microstructures, grain size distributions, texture and misorientation distributions were performed using electron backscattered diffraction in a field emission gun scanning electron microscope. The results were compared with conventional (symmetric) rolling carried out under the same conditions of temperature and strain rate. Simulations of deformation texture evolution were performed using the viscoplastic self-consistent polycrystal plasticity model. The main trends of texture evolution are faithfully reproduced by the simulations for the tests at room temperature. The deviations that appear for the textures obtained at high temperature can be explained by the occurrence of dynamic recrystallization. Finally, the mechanisms of texture evolution in magnesium during asymmetric and symmetric rolling are explained with the help of ideal orientations, grain velocity fields and divergence maps displayed in orientation space.
Materials Science Forum, 2003
The possibility of improving the cold formability of wrought magnesium alloys is considered in light of their good hot forming characteristics. Magnesium alloy AZ31B sheet is selected as a model system. Parameters affecting formability, such as strain hardening rate, strain rate sensitivity, and the degree of anisotropy are examined systematically by conducting tensile tests over a range of temperatures (room temperature to 250ºC) and strain rates (1x10-5 to 0.1 s-1). The plastic anisotropy and deformation texture evolution are examined in samples aligned with the sheet rolling and transverse directions. Polycrystal plasticity simulations using a viscoplastic self-consistent (VPSC) formulation are used to model the observed anisotropy and texture evolution. The adjustable parameters in the model are the relative critical resolved shear stresses of the dislocation mechanisms known to operate within magnesium. The experimental results suggest that an increased strain rate sensitivity is the most important macroscopic change responsible for inducing the formability observed at high temperatures. The polycrystal simulations indicate that an increased activity of non-basal, <c+a> dislocations provides a self-consistent explanation for the observed changes in the rate sensitivity, anisotropy, and texture evolution with increasing temperature.
Modeling texture evolution during hot rolling of magnesium alloy AZ31
Materials Science and Engineering: A, 2007
The texture evolution during hot rolling of the magnesium alloy AZ31 is simulated using a visco-plastic self-consistent model including crystallographic slip, twinning and recrystallization. This combined model is shown to capture the main features observed in mechanical tests and in X-ray diffraction measurements of the texture. The model is implemented in the commercial finite element code ABAQUS/Explicit ® , and hot rolling is simulated. Although the strain field exhibits considerable gradients over the sheet thickness and strong shear components at the sheet surface, the basal texture, as it is commonly observed in rolled magnesium sheets, predominates over the whole thickness.
Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing, 2012
In the present study, asymmetric rolling was carried out for incorporating a shear component during the rolling at different temperatures, and was compared with conventional (symmetric) rolling. The microstructures were investigated using electron back-scatter diffraction (EBSD). The strain incorporated was compared with the help of grain orientation spread (GOS). GOS was eventually used as a criterion to partition the microstructure for separating the deformed and the dynamically recrystallized (DRX) grains. The texture of the partitioned DRX grains was shifted by ∼30 • along the c-axis from the deformed grains. The mechanism of dynamic recrystallization (DRX) has been identified as continuous dynamic recovery and recrystallization (CDRR). The partitioned deformed grains for the higher temperature rolled specimens exhibited a texture similar to the room temperature rolled specimen. The asymmetric rolling introduces a shear component which shifts the texture fibre by ∼5-10 • from the conventional rolling texture. This led to an increase in ductility with little compromise on strength.
Metals, 2021
Binary and ternary Mg-1%Er/Mg-1%Er-1%Zn alloys were rolled and subsequently subjected to various heat treatments to study texture selection during recrystallization and following grain growth. The results revealed favorable texture alterations in both alloys and the formation of a unique ±40° transvers direction (TD) recrystallization texture in the ternary alloy. While the binary alloy underwent a continuous alteration of its texture and grain size throughout recrystallization and grain growth, the ternary alloy showed a rapid rolling (RD) to transvers direction (TD) texture transition occurring during early stages of recrystallization. Targeted electron back scatter diffraction (EBSD) analysis of the recrystallized fraction unraveled a selective growth behavior of recrystallization nuclei with TD tilted orientations that is likely attributed to solute drag effect on the mobility of specific grain boundaries. Mg-1%Er-1%Zn additionally exhibited a stunning microstructural stability ...