Significant improvement of bending properties (approximately 64.7%) for WE43 magnesium alloy was realized by weakening the basal texture and raising the deformation temperature. The mechanisms for such improvement were investigated in detail by combining the experiment and finite element model. The results concluded that the coupling effects of weak basal texture and high deformation temperature was the key reason producing the above improvement of bending properties. Specially, the TD sample with weak basal texture was more conducive to activating basal slip than the RD sample, resulting in its higher strain hardenability and consequently more significant bending properties. Based on weak basal texture, raising the deformation temperature could further improve the bending properties. This improvement mechanism was attributed to the abundant activations of non-basal slip instead of basal slip, which could increase the independent slip systems and efficiently delay the development of the strong basal texture. Moreover, the occurrence of partial DRV and DRX relieved the stress concentrations by consuming the dislocations, further improving the bending properties. The activations of these deformation mechanisms matching the corresponding bending stress states caused the crystal rotation and the texture variety in the bending samples. Basal slip activation aligned the (0002) basal planes parallel to tensile stress in the outer region or perpendicular to compressive stress in the inner region. Additionally, prismatic slip activation induced crystal rotation around the c-axis, developing <10-10>//LD texture in the outer region but <10-10>⊥LD texture in the inner region.

In order to improve the tension-compression asymmetry that exists widely in extruded magnesium alloys, ZK61 magnesium alloys with different texture characteristics were prepared by conventional extrusion, compression-extrusion, and cyclic extrusion compression. The effect of texture on the tension-compression asymmetry and associated deformation mechanisms of magnesium alloys was revealed based on the Sachs assumption. Subsequently, a texture-modified Hall-Petch relationship was used to quantify the combined effect of texture and grain on both tensile and compressive yield strengths. It is found that the slight weakening of the {0002}∥LD fiber texture was beneficial to the suppression of {10‐12} twinning and the activation of prismatic slip, which in turn significantly improved the tension-compression asymmetry without the obvious sacrifice of strength. However, excessive texture inclining can cause a striking decrease in strengths and even reverse tension-compression asymmetry due to the activation of basal slip and pyramidal slip. In conclusion, slight basal texture weakening was a texture optimization strategy to obtain tension-compression symmetry and high strength for wrought magnesium alloys.

In this study, thin-wall Mg-6.03Zn-0.55Zr alloy tubes consisted of fine dynamic recrystallized (DRXed) grains and ultrafine grains were successfully obtained by hot spinning process. The results showed that the microstructures of the initial extruded tubes were greatly refined with average grain sizes of 4.46-10.32 mu m (300-450 degrees C) due to the DRX process, especially at low spinning temperatures. Moreover, the basal texture was transformed from extruded fiber texture to spun tilted plane texture with an angle of similar to 10 degrees deviated from the axial direction (AD). More specifically, the basal texture was weakened along AD but was strengthened along the transverse direction (TD) compared with the extruded texture due to the reduced difficulty in pyramidal slip activation and the shear deformation induced by the rollers. Consequently, the spun Mg-6.03Zn-0.55Zr alloys showed significant yield asymmetry along AD and TD at room temperature and the increase in spinning temperature had a negative influence on yield strength (YS) that the YS along AD decreased from 290 +/- 5 MPa (300 degrees C) to 232 +/- 2 MPa (450 degrees C) and the YS along TD decreased from 236 +/- 6 MPa (300 degrees C) to 198 +/- 4 MPa (450 degrees C). Both texture and grain refinement were the important factors in the mechanical properties according to the Hall-Petch relationship due to the varied activation fractions of deformation modes along AD and TD, especially the activation of prismatic slip. Moreover, the fracture mechanism of the spun alloys consisting of fine DRXed grains and ultrafine grains was unusual. The aggregated ultrafine grains played a negative role in the fracture mechanism, because the ultrafine grains were transformed from the dislocation cells and the micro-crack easily occurred in the ultrafine grains.

A series of hot plane strain compression (PSC) experiments of the extruded Mg-6.03Zn-0.55Zr alloy were conducted on the Gleeble-3500 machine with strain rates of 0.01 s−1 to 10 s−1 and temperatures ranging from 300 °C to 500 °C to reveal the microstructure evolution during the secondary process. The effects of grain refinement and texture modification which were easily affected by the deformation mechanism and dynamic recrystallization (DRX) were systematically studied. Experimental results showed that the main deformation mechanism during PSC was basal slip (74.3 %–94.9 %) and assisted by prismatic slip (4.8 %–21.1 %) and pyramidal slip (0.3 %–4.6 %). Since the pyramidal slip and prismatic slip were more preferred to activate owing to the significant decrease of critical resolved shear stress (CRSS) at a higher temperature, the activation of non-basal slip promoted the c-axes of the grains deviated from compression direction which weakened the basal fiber texture. Moreover, the activation of non-basal slip could promote DRX behavior to some extent. Further analysis of the DRX mechanism showed that the continuous DRX (CDRX) by continuous rotation of low angle grain boundaries was dominant at lower temperatures and higher strain rates, while discontinuous DRX (DDRX) which nucleated at the grain boundaries played a more and more important role as the temperature increased and strain rate decreased. After characterizing the orientations of the DRXed grains, the CDRXed grains owned a similar grain orientation with the deformed grain while the DDRXed grains exhibited a fairly dispersed distribution, indicating that the weakening effect of the basal texture was greater with a higher DDRX fraction.

The pulsed current effect on the bending formability and microstructure evolution of the Mg–2.5Nd–0.5Zn–0.5Zr (wt

采用扫描电镜、 透射电镜、X射线衍射和拉伸试验等技术,研究了不同挤压比制备出的Mg-2.5Nd-0.5Zn-0.5Zr合金的微观组织和力学性能.结果表明,初始材料为近似等轴晶粒,平均晶粒尺寸约为23.8μm,沿晶界析出大量离异的共晶Mg12Nd相,在晶界处共晶相呈连续网状分布.挤压之后合金组织明显细化,E1(挤压比为7.65)和E2(挤压比为12.56)合金平均晶粒尺寸分别为8.1和6.3μm,力学性能显著提高,E1合金沿挤压方向的抗拉强度、 屈服强度和伸长率分别为231 MPa、152 MPa和18.9％;E2合金沿挤压方向的抗拉强度、 屈服强度和伸长率分别为257 MPa、213 MPa和22.4％.E2合金板材的各向异性指数与E1合金相比明显降低,结果表明增大挤压比可以有效缓解Mg-2.5Nd-0.5Zn-0.5Zr合金板材的各向异性.

The microstructural characterization and mechanical behavior of the extruded ZK61 alloy were examined under dynamic and quasi-static loading at 623 K. The microstructure showed that an adiabatic shear band (ASB, similar to 10 mu m in width) was formed under dynamic loading at 3.6 x 10(3) s(-1) due to severe local plastic deformation and it was composed of ultra-fine grains (similar to 0.46 mu m). By comparison, the shear deformation of quasi-static loading was located in an area (similar to 200 mu m in width) with equiaxed grains (similar to 4 mu m). The texture analysis of the shear regions showed a stable orientation that all the (0002) basal plane was parallel to the shear direction (SD) and the orientation mainly aggregated near < 10-13 >//SD, while a weak peak around < 0001 >//SD appeared with a strain rate of 1.0 x 10(-3) s(-1). The main recrystallization mechanism during quasi-static deformation was discontinuous dynamic recrystallization (DDRX) which nucleated at the grain boundaries by absorbing surrounding highdensity dislocations. However, the formation of the DRXed grains within the ASB during dynamic deformation was attributed to rotational dynamic recrystallization (RDR) that the sub-grain boundaries tilted nearly 30. to generate new grains driven by the grain boundary energy. For mechanical responses, the stress-strain curve of dynamic loading showed high yield stress and long working-hardening stage, while the strain-hardening and thermal-softening in quasi-static curves reached a dynamic balance.

The effects of different extrusion ratios (7.6, 12.5 and 26.1) on the microstructure evolution, texture characteristics and mechanical properties of Mg-2.5Nd-0.5Zn-0.5Zr (wt.%) alloys have been systematically studied. The results showed that with the increase of extrusion ratio, the dynamic recrystallization grain size decreased first and then increased, the texture state changed from weakened bimodal texture to strong basal texture with the texture strength increased from 6.7 to 19.4. The growth of grain size was mainly attributed to rise of temperature transformed by the deformation heat with high extrusion ratio and the more intense extrusion deformation. The mechanical properties of the alloy increased first and then decreased with the increase of the extrusion ratio. When the extrusion ratio was 12.5, the alloy exhibited excellent mechanical properties. The higher yield strength results from the interaction of refinement strengthening, dislocation strengthening, precipitation strengthening and texture strengthening. With the increase of extrusion ratio, the proportion of basal slip increased gradually when the alloy was tensile in extrusion direction, and the deformation mechanism was mainly basal slip. When the alloy was tensile along the transverse direction, the proportion of basal slip decreased, and the proportion of prismatic slip increased gradually. The main deformation mechanism were basal slip and prismatic slip.

The microstructure evolution, mechanical response and deformation mechanism of the extruded Mg2.5Nd-0.5Zn-0.5Zr alloy sheet by high-temperature (423-573 K) tensile were investigated. The results showed that the alloy exhibited excellent high-temperature mechanical properties at 523 K (extrusion direction (ED): ultimate tensile strength (UTS)~191.5 MPa, yield strength (YS)~154.5 MPa, elongation (EL) ~30.1%; transverse direction (TD): UTS~190.5 MPa, YS~148.2 MPa, EL~35.2%). The YS of ED and TD of the alloy decreased linearly, and the anisotropy of the alloy decreased gradually (from 0.9261 to 1.009) with the increase of tensile temperature, which was beneficial to the subsequent processing of the alloy. Moreover, the decreased anisotropy was the result of grain size, second phase particles size and texture state. The microstructure showed obvious deformed structures at 423 K and it was gradually replaced by dynamic recrystallization with an average grain size of 3.3-4.2 mu m and the texture strength weakened greatly (maximum pole density value reduced from 15.8 to 4.0) as the temperature increased to 573 K. Meanwhile, both the deformation models and the contributions of different deformation mechanisms at different tensile temperatures were roughly estimated. It was found that basal slip was always the main deformation mechanism at different tensile temperatures, but its contribution to deformation decreased with increased tensile temperatures (from 93.0% to 66.6%). With the increase of tensile temperature, the degree of prismatic slip (from 4.1% to 23.2%) and pyramidal slip (from 2.9% to 10.2%) in deformation gradually increased. (c) 2022 Elsevier B.V. All rights reserved.

A superior combination of the ultra-high tensile strength ( 419.9 MPa), the yield strength ( 376.9 MPa) and the elongation ( 14.8

Isothermal hot compression experiments were conducted on Mg-2.5Nd-0.5Zn-0.5Zr alloy to investigate hot deformation behavior at the temperature range of 573–773 K and the strain rate range of 0.001 s−1–10 s−1 using a Gleeble-3500D thermomechanical simulator. The results showed that the rheological curve showed a typical work hardening stage, and there were three different stages: work hardening, transition and steady state. A strain compensation constitutive model was established to predict the flow stress of the Mg-2.5Nd-0.5Zn-0.5Zr alloy, and the results proved that it had high predictability. The main deformation mechanism of the Mg-2.5Nd-0.5Zn-0.5Zr alloy was dislocation climbing. The processing maps were established to distinguish the unstable region from the working region. The maps showed that the instability generally occurred at high strain rates and low temperatures, and the common forms of instability were cracking and flow localization. The optimum machining range of the alloy was determined to be 592–773 K and 0.001–0.217 s−1. With the increase in deformation temperature, the grain size of the alloy grew slowly at the 573–673 K temperature range and rapidly at the 673–773 K temperature range.

The microstructures evolution, texture characteristics and mechanical properties of Mg-2.5Nd-0.5Zn-0.5Zr alloy processed by high strain rate rolling (HSRR) at different temperature were systematically investigated in the current study. The results showed that the initial material was approximately equiaxed grains (23.8 mu m) with a large number of divorced eutectic Mg12Nd phases precipitated along grain boundaries in a continuous network. After HSRRed, the microstructure was obviously refined, and uniform distributed. The average grain size was refined to 3.63 mu m (R673), 2.71 mu m (R648) and 2.17 mu m (R623), respectively, and corresponding percentage of recrystallization were 46.1%, 49.3% and 63.9%, respectively. R623, R648 presented a strong (0002) basal surface bimodal texture in the RD direction but this texture was in the TD direction in R673, all of which preferential orientation was at 66.3-90 degrees region. An excellent combination of ultimate tensile strength (324 +/- 2 MPa), the yield strength (298 +/- 3 MPa) and the elongation (6.9 +/- 1.5%) were achieved in a fine-grained (2.17 +/- 1.17 mu m) Mg-2.5Nd-0.5Zn-0.5Zr alloy prepared by HSRR at 623 K. The higher yield strength can be obtained by refinement strengthening, dislocation strengthening, precipitation strengthening and texture strengthening.

Fine-grained, high-strength and high-ductility Mg-2.5Nd-0.5Zn-0.5Zr alloy sheets were prepared by multi-pass hot rolling with ultimate tensile strength of 311.9 MPa, yield strength of 272.4 MPa, elongation of 17.1%, and the average grain size of 4.25 μm. After multi-pass hot rolling, all plates showed the characteristics of bimodal rolling direction-tilt texture (with the basal poles tilting at about ±15–20° form normal direction towards rolling direction). With the increase of rolling passes, the basal texture strength decreased gradually, which was 9.5 (1st pass), 7.5 (2nd pass) and 5.4 (3rd pass), respectively. The ductility improvement was the result of the interaction of texture weakening, basal slip and non-basal slip actuation.

The microstructures, texture, damping and mechanical properties of Mg-Nd-Zn-Zr alloy processed by hot extrusion were investigated in this work. The results showed that the microstructures were markedly refined, and uniformly distributed after hot extrusion. The average grain size was refined to 8.1 ± 1.6 μm (extrusion ratio was 7.65, E1) and 6.28 ± 1.7 μm (extrusion ratio was 12.56, E2), respectively, and the yield strength of the alloy was increased significantly. The dislocation density and texture of the alloy increase with the increase in the extrusion ratio. The damping values Q−1 of as-cast (Initial), E1 and E2 alloys were 0.03504, 0.01634 and 0.01539 at the strain of 1 × 10−3, respectively. Mg-Nd-Zn-Zr alloy could be classified as high strength (259 MPa), high plasticity (21.4%) and high damping (0.01539) Mg alloy.

Tension/compression symmetrical ZK61 magnesium alloy rod with fine grain and weak texture was achieved by compression-extrusion process. The formation mechanism of fine grain and weak texture was analyzed by investigating the microstructure and texture evolution during compression-extrusion process. In compression stage, {10–12} twinning deformation was activated greatly, which brought about significant grain refinement and formation of <0002>∥ED texture. As extrusion process going on, twinning gradually decreased and basal slip dominated the following deformation. Texture oriented into single annular shape by subsequent twinning in early extrusion and the annulation rotated toward ED gradually then merged into fiber texture by basal slip in late extrusion. Besides, texture was weakened by grain boundary slip and non-basal slip. With DRXed grain orientations similar to that of the deformed parent grains, Discontinuous dynamic recrystallization played a dominant role in grain refinement during extrusion stage, but the refinement was relatively minor compared to twining refinement in compression stage. Finally, magnesium alloy with fine grain and weak texture was achieved. The benefit of this microstructure and texture characteristic upon mechanical properties was the great enhancement of compressive yield strength, from the suppression of twinning when compressed. Therefore, tension/compression asymmetry was greatly improved by compression-extrusion process.