Grains Of Magnesium Alloy Research Articles

Revealing the effect of misorientation on the deformation behavior of a Mg-Y alloy from the perspective of local strain

The addition of rare earth (RE) elements in magnesium alloys may significantly enhance the ductility of magnesium alloys, which is generally attributed to the decrease of stacking fault energy, the reduced critical resolved shear stress (CRSS) differences among different deformation modes and the weakening of basal texture. Rare earth elements also change the misorientation between adjacent grains of magnesium alloy, whose effects on the deformation behavior and thus the ductility of magnesium alloy were not emphasized before. In this work, ex-situ high-resolution digital image correlation (HR-DIC) coupled with electron backscatter diffraction (EBSD) was used to reveal the effect of the misorientation on the deformation behavior of a Mg-Y binary alloy from the perspective of local strain. It is shown that the heterogeneity of local strain is largely dependent on the misorientation between adjacent grains. For the intergranular deformation, three scenarios are observed, namely strain transfer, strain concentration and suppressed deformation, which mainly occurs at low misorientation, moderate misorientation and high misorientation, respectively. In addition, much more non-basal slip is found to be activated near the grain boundaries with moderate misorientation angles due to the high geometric compatibility factor (m’B-Pr/Py), which is favorable for the intergranular deformation compatibility, thus reducing the strain concentration near grain boundaries and achieving high ductility. For the intragranular deformation, a wide range of misorientation between adjacent grains in the Mg-Y alloy causes multiple basal slip systems to be activated within a grain, which also facilitates work hardening, thus contributing to improving ductility. Therefore, tailoring the misorientation between adjacent grains may be an effective way to improve the ductility of magnesium alloys.

Simulation study on the texture evolution mechanism of magnesium alloy cylindrical parts with inner ribs during hot power spinning

Grasping the mechanism of texture evolution during hot power spinning of magnesium alloy cylindrical parts with inner ribs, which have the dual lightweight advantages of material and structure, can provide a theoretical basis for texture regulation in the preparation of high-performance magnesium alloys. Based on the crystal plastic finite element method, the macro-meso coupled model was constructed and the simulation study of magnesium alloy cylindrical parts with inner ribs during hot power spinning was carried out. The texture evolution mechanism at the position of cylindrical wall (CW) and inner rib (IR) was revealed by tracking the change of grain orientation and the analysis of Schmid factor (SF). The results show that the c-axis of grains of magnesium alloy extruded blank gradually deflects from parallel to tangential direction (TD) to parallel to radial direction (RD). Under the action of radial compressive stress, the formation of texture at CW is attributed to the orientation deflection of grains which have larger SF of basal slip system and locate in the region of the maximum texture strength of blank, while the origin of the texture at IR mainly comes from the orientation deflection of grains with a smaller (0.1~0.2) SF of basal slip system.

Formation of ultrafine grains in magnesium alloy during dynamic extrusion at room temperature

Magnesium alloy is a class of lightweight structural materials with promise for many applications. Here, the authors report a significant grain refinement, high deformation twin density and obvious nanograined structures in magnesium alloy through a novel high strain rate plastic deformation method—dynamic extrusion. By using finite element simulation and transmission electron microscopy (TEM), the authors find that the stain rate during plastic deformation affects the microstructure evolution process, which results in the dynamic deformation mechanisms transition. The results are of interests not only for understanding the deformation mechanisms under dynamic plastic deformation but also for nanostructures formation of the magnesium alloy.

Numerical and experimental studies on solidification of AZ80 magnesium alloy under out-of-phase pulsed magnetic field

For obtaining the finer grains of magnesium alloy, a novel combined pulsed magnetic field with different initial phases, also called out-of-phase pulsed magnetic field (OPPMF), was applied to study the solidification structure of AZ80 magnesium alloy. The numerical simulation was simultaneously conducted to investigate the refinement mechanisms. The experimental results showed that the macrostructure could be effectively refined by applying external magnetic field. Meanwhile, finer grains were obtained with the higher current intensity. However, the increase of current intensity could only refine the grains to about 0.5 mm. Furthermore, compared to a single pulsed magnetic field (PMF) and alternating series of OPPMF (Connection II), a finer structure was observed when the consecutive series of OPPMF (Connection I) was imposed. In contrast with a single PMF and Connection II, the numerical results showed that the greater axial Lorentz force was obtained under the Connection I, generating the stronger forced flow in the melt. It is believed that abundant nuclei could detach from the mold wall and move faster into the interior melt due to the stronger forced flow; besides, the lower superheat and greater temperature uniformity in bulk melt were realized, accounting for the finest structures under the Connection I.

Tailoring texture and refining grain of magnesium alloy by differential speed extrusion process

Magnesium alloy sheets were processed by conventional extrusion (CE) and differential speed extrusion (DSE). The velocity evolutions of DSE sheets at near-surface and mid-layer region are different due to the extra asymmetric shear deformation. This simple shear enforces the near-surface microstructure to exhibit more dynamically recrystallized grains having the c-axis tilted about ±12° toward the extrusion direction. Grain refinement and tilted weak basal texture obtained by DSE process dramatically enhance the room temperature strength and plasticity of the extruded Mg alloy sheets.

Evolution of internal strain during plastic deformation in magnesium matrix composites

Synchrotron radiation diffraction during in situ tensile tests has been used to evaluate the internal elastic strains within the grains of magnesium alloy, AZ31, unreinforced and reinforced with 5 and 10% volume of SiC particles. Composites present initial thermal residual stresses, which are positive (tensile) in the matrix and negative (compressive) in the reinforcing particles. Internal elastic strains evolve in a similar behaviour in the unreinforced AZ31 and in both composites. However, the accumulated elastic strains are reduced in the case of the composite because a part of the applied load is borne by the ceramic particles.

Dynamic Nucleation of New Grains in Magnesium Alloy during Hot Deformation

Dynamic Nucleation of New Grains in Magnesium Alloy during Hot Deformation