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A cup-shaped Mg-Gd-Y-Zr alloy component has been successfully prepared by using the severe plastic deformation (SPD) technique of rotating backward extrusion (RBE), and the microstructure evolution and mechanical properties of different regions along the radial direction have been studied. In addition, the dynamic recrystallization (DRX) mechanism during the deformation process was further analyzed. The results indicate that the grain refinement effect significantly increased from the edge side to the inner side along the wall thickness direction. After RBE deformation, the average grain size of the sample decreased from ~ 106.01 µm in the initial state to ~ 8.55 µm in the innermost region of the cup wall. Many small and dispersed particle phases were distributed at the grain boundaries, and the DRX fraction reached 75.8%. Continuous dynamic recrystallization and discontinuous dynamic recrystallization occurred simultaneously. Due to the random orientation of the grains that underwent DRX, the texture intensity of the alloy was weakened. The microhardness and tensile properties of the alloy were tested along the wall thickness direction, and the fracture morphology was observed. The inner region exhibited the most excellent comprehensive mechanical properties, with yield strength, ultimate tensile strength, and elongation values of 323 MPa, 370 MPa, and 11.3%, respectively. [ABSTRACT FROM AUTHOR]

As a new type of plastic-forming technology, rotary extrusion has the advantages of increasing the hydrostatic stress inside the deformed body and obtaining severe plastic deformation, which creates favorable mechanical conditions for repairing cavity defects. In this article, Deform-3D finite element software is used to establish the finite element model of cavity closure during rotary extrusion and analyze the cavity closure process. The influence of extrusion speed and rotation speed on the evolution of spherical cavity defects was studied, and the critical condition of cavity closure in magnesium alloy during rotary extrusion was obtained. Based on Z-C model and numerical simulation, the adaptability of the model under different parameters was analyzed, and a spherical cavity evolution model suitable for AZ80 magnesium alloy rotary extrusion was constructed to predict the change of cavity closure volume. The physical experiment of cavity closure in rotary extrusion was carried out on a Gleeble-3500 thermal simulator, which verified the accuracy of the numerical simulation and cavity evolution model and provided theoretical guidance for improving the performance of rotary extrusion products and related research. [ABSTRACT FROM AUTHOR]

Based on the deforming technique of severe plastic deformation (SPD), the grain refinement of a Mg-9Gd-3Y-2Zn-0.5Zr alloy treated with decreasing temperature reciprocating upsetting-extrusion (RUE) and its influence on the mechanical properties and wear behavior of the alloy were studied. The RUE process was carried out for 4 passes in total, starting at 0 °C and decreasing by 10 °C for each pass. The results showed that as the number of RUE passes increased, the grain refinement effect was obvious, and the second phase in the alloy was evenly distributed. Room temperature tensile properties of the alloy and the deepening of the RUE degree showed a positive correlation trend, which was due to the grain refinement, uniform distribution of the second phase and texture weakening. And the microhardness of the alloy showed that the microhardness of RUE is the largest in 2 passes. The change in microhardness was the result of dynamic competition between the softening effect of DRX and the work hardening effect. In addition, the wear resistance of the alloy showed a positive correlation with the degree of RUE under low load conditions. When the applied load was higher, the wear resistance of the alloy treated with RUE decreased compared to the initial state alloy. This phenomenon was mainly due to the presence of oxidative wear on the surface of the alloy, which could balance the positive contribution of severe plastic deformation to wear resistance to a certain extent. [ABSTRACT FROM AUTHOR]

An increase in hydrostatic stress improves the plasticity of metallic materials. However, for some special components, such as large thin-walled components with high ribs, excessive hydrostatic stress can cause several problems that make it impossible to prepare such components using plastic forming methods. In this study, the effect of hydrostatic stress on the deformation behavior of large thin-walled components with high ribs was investigated using a combination of numerical simulations and theoretical derivations. The results indicated that excessive hydrostatic stress leads to die failure, causing metal flow difficulties, uneven deformation, inconsistent mechanical properties, and reduced forming accuracy. Therefore, a low-hydrostatic-stress extrusion method was proposed by adjusting the contact friction, metal flow direction and displacement, and force boundary conditions to reduce the hydrostatic compressive stress. These principles are mainly reflected in the following three aspects: First, the size of the difficult deformation zone was reduced by changing the friction conditions from dry friction to fluid friction or boundary friction to reduce the frictional resistance. Second, the high-stress zone was eliminated by changing the metal flow direction, adjusting the strain state from unidirectional to multi-directional flow, shortening the metal flow path, and reducing the metal flow resistance. Third, the strong compressive stress state in the three directions was weakened by regulating the force boundary conditions and changing the loading method from one-way extrusion to multi-directional loading. Based on these principles, a series of new forming technologies have been developed, such as actively counteracting frictional resistance, slotting, and ditching on dies for long-lasting lubrication, multi-directional short-range metal flow, drawing-assisted extrusion, and multi-directional active loading. The adoption of these technologies realizes the labor-efficient formation of large thin-walled components with high ribs and provides the formed members with high precision and uniform mechanical properties. [Display omitted] • The influences of hydrostatic stress on metal flow, forming forces and strains were revealed. • The principle of low hydrostatic stress extrusion was developed, which can be employed to reduce the working stress. • The forming force was reduced, and the deformation uniformity and forming accuracy of thin-walled components were improved. [ABSTRACT FROM AUTHOR]

The spark plasma-sintered Ti-6Al-4V alloy was used as experimental specimens to perform the multi-pass hot compression. The deformation temperature was 950, 900, 850 °C, and the compressed amount was 20, 30, 20% corresponding to one pass, two passes and three passes, respectively. The flow behaviors revealed that the curve with the strain rate of 5 s−1 appeared obvious oscillatory phenomenon after peak. Additionally, the curve with strain rate of 0.1 and 1 s−1 almost kept constant after peak stress during the process of two-pass compression. The microstructures showed that the sintered voids with the average diameter of 7.53 μm could be observed in initial Widmanstatten structures with the aspect ratio of 11.49 ± 0.5. The deformed inhomogeneity had prominent influence on the microstructures. For three-pass deformation with the strain rate of 0.1 s−1, the microstructures of severe plastic deformation area were equiaxial microstructures with the grain diameter of 3.82 μm, while the microstructures for medial and small plastic deformation area were dual and Widmanstatten, respectively. With the strain rate of 0.1 s−1, the fraction of dynamic recrystallization (fDRX) increased from 0.034 through 0.112 to 0.440 with the passes increased, and the variation tendency toward average diameter of grain size versus compressed passes shifted reversely. The β→α phase transformation was the main reason for the misorientation angle nearby 60° for one pass with the strain rate of 0.1 s−1. The fDRX declined from 0.440 through 0.225 to 0.297 with raising the strain rate for three-pass deformation, but the grain size changed oppositely. The CDRX and DDRX were both appeared during multi-pass hot deformation. [ABSTRACT FROM AUTHOR]

This paper provided an efficient single pass severe plastic deformation (SPD) method, annular channel angular extrusion (ACAE), for fabricating AZ80 magnesium alloy shell part. The effect of ACAE process on the microstructure homogeneity, texture, and mechanical properties of extruded part was experimentally investigated. For comparison, conventional backward extrusion (BE) was also conducted on processing AZ80 part with same specification. The results showed that ACAE process has a better capacity to refine the microstructure and dramatic improve the deformation homogeneity of the extruded part than BE process. Due to two strong shear deformations were implemented, ACAE process could also concurrently modify the basal texture more notably than BE process. In particular, a bimodal texture was found in ACAE extruded part, which was greatly related to the enhanced synergetic action of basal slip and secondary slip caused by the effective shear stress. More uniform and superior hardness along the thickness and height of part were achieved via ACAE process. Further surveying of tensile tests also showed that the part fabricated by ACAE process exhibited significantly higher and far more homogeneous tensile properties with an excellent balance of strength and ductility. The remarkable enhanced tensile properties of ACAE extruded part could be primarily attributed to the significant grain refinement, which provided a powerful grain boundary strengthening effect and meaningfully suppressed the development of twin-sized cracks during tensile deformation. It was established that ACAE process seemed to be a very promising single pass SPD method for manufacturing Mg-based alloy shell parts with more homogeneous microstructure and superior performance. [ABSTRACT FROM AUTHOR]

• Proposing an extended process based on CEC - ECC. • Investigating the effect of backpressure on strain in the ECC process. • Effect of strain on recrystallization and tensile mechanical properties. The capability of a novel severe plastic deformation method for extrusion compression composite processing was investigated. Deform-3D software was used to study the effect of back pressure on the strain distribution of a workpiece by simulating the forming process with and without back pressure. The Mg-12.5Gd-4Y-2Zn-0.5Zr alloy was used to analyze the effect of strain on microstructure and mechanical properties. Results showed that back pressure led to the uniform strain distribution of the deformed workpiece and the decrease in the effective strain standard deviation from 0.73 to 0.68. With increasing strain, the grain size tended to decrease and then increase, contrary to the recrystallization rate trend. The tensile strength gradually increased with increasing strain, but the elongation change trend was changed due to the influence of the bimodal structure. [ABSTRACT FROM AUTHOR]

Abstract Repetitive upsetting-extrusion (RUE), a severe plastic deformation, was performed on the Mg-12.0Gd-4.5Y-2.0Zn-0.4Zr (wt %) alloy at different deformation temperatures in the range of 693–773 K for 1, 2 and 3 passes. The study was aimed to determine the effects of deformation temperatures and processing passes of RUE on the microstructure and texture evolution of the RUEed alloy. It is found that dynamic recrystallization (DRX) occurred in the alloy and β- Mg 5 (Gd,Y,Zn) phase particles precipitated at grain boundaries during the RUE processing. The microstructure was refined remarkably during RUE, the microstructure distribution became more homogeneous and the degree of DRX was increased with the number of the processing passes increasing. The grain refinement was mainly caused by DRX, and the LPSO phases stimulated the DRX around the grain boundaries via particle stimulation nucleation mechanism. The microstructure and texture evolution were mainly depended on the RUE processing parameters, such as processing passes and deformation temperatures. The basal texture was gradually weakened during more processing passes and higher deformation temperatures of RUE processing. The microstructure and texture evolution of the alloy were affected more by processing passes than deformation temperatures during RUE. After 3 RUE passes, some (0001) basal planes were perpendicular to the ED and that also were parallel to the ED in some grains, which is different from that observed in both extruded alloys and other plastically deformed counterparts. The number fraction of low angle grain boundaries tended to decrease while the average misorientation angles tended to increase with the processing passes and deformation temperatures of the RUE increasing. Highlights • The Mg-Gd-Y-Zn-Zr alloy was processed by RUE under different conditions. • The microstructure and texture evolution during RUE were investigated. • The DRX occurred in the alloy during the RUE. • The microstructure and texture were affected more by passes than temperatures. [ABSTRACT FROM AUTHOR]

The cylindrical tubular parts of a high-strength magnesium alloy were processed by a novel severe plastic deformation method (rotary extrusion: RE) at the same strain rate and deformed temperature under various revolutions. The effects of this process on the grain refinement and microhardness of the Mg-12Gd-4.5Y-2Zn-0.4Zr alloys were investigated. The results demonstrated that the tube microhardness decreased as the rotary revolutions increased, whereas the matrix and the second phases became significantly homogeneous. The dynamic recrystallization occurred in the RE process. When the temperature and the strain rate were constant, the grains increased in size as the revolutions increased, whereas the dynamic recrystallization refinement and the grain growth were in dynamic competitive relationships. [ABSTRACT FROM AUTHOR]

In this study, a new rolling-extrusion technology implementing plastic deformation is presented for the forming of the hollow cylindrical component, and the design criterion of the rollers with changeable internal diameter is introduced based on the prediction of the forward slip value. Moreover, in order to investigate the feasibility of this technology, a finite element (FE) simulation and an experiment are conducted. The result of the FE simulation shows that: the metal flow is caused only in the area where the rollers contact the billet, and influenced by the heat exchange between the billet and the rollers; a set of most reasonable technological parameters is selected through an evaluation of the deformation uniformity of 18 groups of simulations. In addition, the result of the experiment shows that the hollow cylindrical component can be formed, and the consumption for the material of each component can be saved at least 16.8 %. [ABSTRACT FROM AUTHOR]

The thermal deformation behaviour of Mg-9Gd-4Y-2Zn-0.5Zr alloy at temperatures of 360–480 °C, strain rates of 0.001–1 s−1 and a maximum deformation degree of 60% was investigated in uniaxial hot compression experiments on a Gleeble 3800 thermomechanical simulator. A constitutive equation suitable for plastic deformation was constructed from the Arrhenius equation. The experimental results indicate that due to work hardening, the flow stress of the alloy rapidly reached peak stress with increased strain in the initial deformation stage and then began to decrease and stabilize, indicating that the deformation behaviour of the alloy conformed to steady-state rheological characteristics. The average deformation activation energy of this alloy was Q = 223.334 kJ·mol−1. Moreover, a processing map based on material dynamic modelling was established, and the law describing the influence of the machining parameters on deformation was obtained. The experimental results indicate that the effects of deformation temperature, strain rate and strain magnitude on the peak dissipation efficiency factor and instability range were highly significant. With the increase in the strain variable, the flow instability range increased gradually, but the coefficient of the peak power dissipation rate decreased gradually. The optimum deformation temperature and strain rate of this alloy during hot working were 400–480 °C and 0.001–0.01 s−1, respectively. [ABSTRACT FROM AUTHOR]

Rotating backward extrusion (RBE) is one of severe plastic deformation (SPD) methods used to produce cylindrical components with a very large strain by a single pass. In this study, the microstructure and texture evolution in the different regions of Mg-12Gd-4Y-2Zn-0.5Zr (wt.%) alloys via RBE process were investigated by using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron back-scatter diffraction (EBSD). The results showed that the cup-shaped sample formed by RBE process exhibited typical gradient microstructure expanding from its inner wall to outer wall along the radial direction (RD). The average grain size of the RBEed sample decreased when the radius decreased from the edge region to the center region along the RD, which was attributed to the different strains and strain rates in the different regions. It also could be observed that the center region showed highest deformation and the edge region exhibited the lowest deformation in the RBEed sample along the RD. In addition, the grain refinement mechanisms of the experimental alloy containing long-period stacking ordered (LPSO) phases after RBE with 100 N were continuous dynamic recrystallization (CDRX), discontinuous dynamic recrystallization (DDRX) and particle stimulated nucleation (PSN). [ABSTRACT FROM AUTHOR]

The quasi-static and low cycle fatigue tests of extruded 7075 Al alloy (Φ200 mm) were investigated in three directions: the extrusion direction (ED), the radial direction (RD), and 45° with ED (45°). Grain morphology analysis, texture measurement, and fatigue fracture characterization were conducted to discuss the relationship between microstructure and mechanical properties. The experimental results showed that the ED specimen had higher ultimate tensile strength (UTS) and low cycle fatigue (LCF) properties, which were mainly attributed to the following three causes. First, the grain boundaries (GBs) had an obvious effect on the crack growth. The number of GBs in the three directions was different due to the shape of the grains elongated along the ED. Second, the sharp <111> texture and the small Schmidt factor along the ED explained the higher ultimate tensile strength (UTS) of the ED specimens. Third, fatigue fracture observation showed that the ED specimen had a narrow fatigue striation spacing, which indicated that the plastic deformation of the ED specimen was the smallest in each cycle. In addition, two fatigue prediction models were established to predict the LCF life of extruded 7075 Al alloy, based on the life response behavior of the three directions under different strains. [ABSTRACT FROM AUTHOR]

The rotating backward extrusion (RBE) process, as a new severe plastic deformation (SPD) process, is based on conventional backward extrusion and rotation, which meets the requirement of modern industrial development with its high performance and production efficiency. However, there is little research on the microstructure evolution and texture modification of the RBE process. Thus, in this study, the effect of different rotating revolutions, e.g., n = 5, n = 10, and n = 50, on the microstructure and texture development for the RBE process based on the AZ80 magnesium (Mg) alloy were investigated at 653 K. The results disclose that the rotating revolution is an influencing processing parameter on the deformation of the RBE process. The grain refining ability is enhanced with the increase of the rotating revolutions, and the minimum grain size of the cup bottom, shearing zone, and cup wall can reach to 16.7 μm, 15.6 μm, and 13.0 μm, respectively, under the condition of n = 50. Furthermore, with the increase in the rotating revolutions, the microstructure of the alloy becomes more uniform and the proportion of dynamic recrystallization (DRX) is also increased. The maximum DRX fractions of the sample for the cup bottom and cup wall are 95.4% and 86.8%, respectively, at n = 50. The DRX mechanism of the RBE process is determined by the continuous DRX and discontinuous DRX. In addition, the texture can be significant weakened during the RBE process, especially at the cup bottom, where the maximum pole intensity can be reduced from 17.6 at n = 10 to 6.5 at n = 50, which can be attributed to the higher proportion of new DRXed grains whose orientations are more random compared with the deformed grains. [ABSTRACT FROM AUTHOR]

In the current work, cyclic expansion extrusion with an asymmetrical extrusion cavity (CEE-AEC), as a relatively novel severe plastic deformation method, was applied to fabricate an AZ31B magnesium alloy plate with a size of 50 × 100 × 220 mm, and the resultant microstructure, texture development, and mechanical properties were systematically investigated. A refined and homogeneous grain structure was achieved after three passes of deformation due to dynamic recrystallization. The grain refinement degree in comparison to as-cast alloys was more than ~96%. With the increasing number of CEE-AEC passes, a basal inclination texture was gradually formed, with the basal planes inclined ~45° from the transverse direction to the extrusion direction, which could be attributed to the introduction of an asymmetrical extrusion cavity that led to an increasing Schmid factor for the activation of basal slip systems. The comprehensive mechanical properties were improved by successive multi-passes of CEE-AEC processing, especially due to the ductility reaching to 30.0 ± 1.3% after three passes of deformation. The competition between the grain refinement and texture modification were the main strengthening mechanisms. [ABSTRACT FROM AUTHOR]

In this paper, cyclic expansion extrusion with an asymmetrical extrusion cavity (CEE-AEC) was proposed as a novel severe plastic deformation process for fabricating bulk ultrafine-grained (UFG) metals. Increasing the size of the processed sample and introducing the shear strain by attaching an asymmetrical extrusion cavity are the core advantages of this technology. The CEE-AEC process was applied to Mg-13Gd-4Y–2Zn-0.4Zr alloys for four passes deformation with the decreasing temperature, and then the microstructure evolution, texture analysis, and mechanical properties were investigated. Microstructure results show that a dramatical grain refinement is achieved from initial value of 24 ± 0.3 μm to 1.4 ± 0.3 μm which is mainly led by continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) as well as the particle-stimulated nucleation (PSN) induced by interdendritic long-period stacking ordered (LPSO) phases. With increasing CEE-AEC passes, the intensities of basal texture are gradually weakened, and the basal plane tends to incline to transverse and normal directions with different degrees of different passes, leading to a remarkable increase in Schmid factor for the activation of basal slip system. Tensile tests at room temperature (RT) indicate that the samples after three-passes of CEE-AEC exhibit the best comprehensive mechanical properties with tensile yield strength (TYS) of 302 MPa, ultimate tensile strength (UTS) of 330 MPa, and fracture elongation of 6.1%, which are mainly ascribed to the grain refinement, broken of interdendritic block-shaped LPSO phases, and texture modification. • A novel SPD method entitled CEE-AEC was proposed. • The Mg-13Gd-4Y–2Zn-0.4Zr alloy was processed by CEE-AEC with consecutive four passes deformation. • A significant grain refinement from initial 24 ± 0.3 μm to 1.4 ± 0.3 μm was obtained. • Continuous and discontinuous dynamic recrystallizations took place during CEE-AEC. • The mechanical properties were contributed from the competitive of fine grains strengthening and texture modification. [ABSTRACT FROM AUTHOR]

Annular channel angular extrusion has been recently developed as a new single-pass severe plastic deformation method suitable for producing large size cup-shaped parts from cylindrical billets. In this study, the novel technology was successfully applied to commercial AZ80 Mg alloy at 300 °C, and microstructure, texture evolution, and mechanical properties were investigated. Due to severe shear deformation, the initial microstructure, including the coarse grains and large eutectic β-phases, was greatly refined. The strong basal texture formed during the initial deformation stage was modified into a weak tilted dynamic texture. During the deformation process, fine β-particles separated from eutectic phases effectively hindered the grain boundary migration and rotation, enhancing the grain refinement and texture weakening. More than 63% of the microhardness increase was achieved in this extruded part. Also, tensile tests showed the yield strength and elongation in both directions (transverse and longitudinal) of extruded part were improved more than 2.5 times, and the ultimate tensile strength was improved more than 2 times, compared to the initial material state. The improved material properties were mainly attributed to microstructure (grain and phase) refinement and texture weakening. It was demonstrated that the annular channel angular extrusion process can be considered as a novel and effective single-pass severe plastic deformation method. [ABSTRACT FROM AUTHOR]

Lightweight equipment in aerospace and other fields urgently requires magnesium (Mg) alloys components with high-strength plasticity. For this reason, in this study, a gradient heterogeneous structure containing nanocrystallines was constructed successfully using a severe shear deformation process that combines severe plastic deformation techniques and torsional deformation characteristics. The evolution of the microstructure and hardness of Mg-12.12Gd-4.2Y-2.28Zn-0.36Zr (wt%) alloys prepared by severe shear deformation with changes in deformation temperature were investigated. The gradient heterogeneous structure of the alloys formed naturally under high hydrostatic pressure and severe shear stress, and its thickness increased with the deformation temperature. With the application of shear stress, a large amount of rotational dynamic recrystallization (RDRX) behavior occurs in the alloys, refining the coarse initial grains (∼126.3 µm) into fine grains (∼2.03 µm) or even ultrafine grains (∼1 µm). During the RDRX process, low angle grain boundaries (LAGBs) began to form at high distorted grain boundaries and unique lamellar structures, followed by a rapid expansion into the interior of the grains, which ultimately results in the grains being completely covered by subgrains. Meanwhile, the continuously broken long-period stacking-ordered (LPSO) phase and the precipitated bright rare earth rich (RE-rich) phase provide a large number of nucleation sites, further promoting the refinement process of the grains. Subsequently, the grains were further refined to nanocrystallines through the formation and rotation of subgrains under continuous loading of stress. The massive formation of nano-precipitated phases (β phases) along grain boundaries were accompanied by the complete disappearance of other types of second phases. The sources of β phases formation include the layer-by-layer decomposition of the cellular phases and the dissolution/re-precipitation of the LPSO phases. In addition, the introduction of shear stress promotes the random orientation of the DRXed grains through the extensive activation of pyramidal and pyramidal slip. The hardness of the alloys gradually decreased as the cumulative strain decreased at different deformation temperature conditions. When the deformation temperature was 440°C, the alloys reached a maximum hardness of 127.67 HV, which was nearly 43.5% higher than homogenized alloys. The ultra-high hardness of the alloys prepared by severe shear deformation is mainly attributed to grain boundary hardening, diffusion hardening and hetero-deformation induced (HDI) hardening. • Gradient heterostructures can be naturally constructed by severe shear deformation and the intense plastic deformation zone can reach 2.4 mm. • A large number of NM particles are obtained by the layer-by-layer decomposition of the cellular phase and dissolution/re-precipitation of the LPSO phase, which are pinned at nanograin boundaries to inhibit grain growth. • The introduction of shear stress promoted the random orientation of grains through the extensive activation of pyramidal and pyramidal slip. • The significant increase in hardness is mainly due to grain boundary hardening, diffusion hardening and HDI hardening. [ABSTRACT FROM AUTHOR]

This study investigated the effects of severe shear (SS) deformation with different revolutions on the microstructures and hardness of Mg-12.12Gd-4.2Y-2.28Zn-0.36Zr (wt%) alloy. Gradient nanostructures formed naturally after SS deformation, and the thickness and number of each gradient layer increased considerably as the number of rotations increased. After deformation, the average grain size of the alloy gradually decreased from 126.3 μm to 500 nm with the increase in cumulative strain, and the size of the secondary phase also decreased. Consequently, the hardness of the alloy increased considerably after SS deformation and reached 121.3 HV, which is nearly 36.4% higher than that of the as-cast alloy. The achievement of fine and ultrafine grains mainly depends on the rotational dynamic recrystallization (RDRX) behavior. Low-angle grain boundaries (LAGBs) rapidly expanded in soft-oriented grains and were accompanied by gradual rotation of subgrains, while expansion in hard-oriented grains was more difficult. Moreover, the origins of LAGBs included not only grain boundaries with a high distortion but also lamellar structures that are characteristic of SS conditions. In addition, all oversized coarse grains were transformed into equiaxed fine grains under the synergistic effect of continuous dynamic recrystallization (CDRX) and particle-stimulated nucleation mechanisms. However, the formation of nanocrystallines differed greatly from that observed for fine and ultrafine grains, in which nanocrystallines were mainly formed by the rotation of substructures composed of high-density dislocation cells. Currently, grain growth is inhibited by pinning a large number of the nano-precipitated phase at nanocrystalline boundaries. • Gradient nanostructures can be naturally constructed by severe shear deformation. • The region of maximum plastic deformation of the alloy increases significantly with increasing cumulative strain. • Grain refinement during the initial deformation is achieved mainly through RDRX mechanism rather than conventional mechanism. • Nano-particles are obtained by the layer-by-layer decomposition of the cellular phase and dissolution/re-precipitation of the LPSO phase. [ABSTRACT FROM AUTHOR]

[Display omitted] • The synergistic effect of strength and ductility of Mg-RE-Zn alloy is significantly improved by changing the repetitive upsetting extrusion deformation paths under the same cumulative strain. • The different contributions of long period stacking ordered phases strengthening and heterogeneous deformation-induced strengthening lead to variations in yield strength in different samples. This study investigated the effects of different repetitive upsetting extrusion (RUE) deformation paths on the microstructures and mechanical properties of Mg-9.32Gd-3.72Y-1.68Zn-0.72Zr (wt%) alloy. Bimodal microstructures were observed in all RUE deformed samples. Increasing the RUE ratio under the same cumulative strain enhanced the dynamic recrystallization (DRX) process, resulting in higher aspect ratios of deformed grains and dynamic precipitation of β phases. The bulk long period stacking ordered (LPSO) phases promoted the DRX process through a particle-stimulated nucleation mechanism, while the β phases hindered the growth of DRXed grains by a pinning effect during deformation. As the RUE ratios increased, the LPSO phase gradually aligned towards the extrusion direction. The R1P3 sample demonstrated the best balance between strength and ductility under small RUE ratio and multi-pass deformation, with ultimate tensile strength, tensile yield strength (TYS), and elongation reaching 382.5 ± 3.1 MPa, 302.3 ± 4.2 MPa, and 8.7 ± 0.5%, respectively. The different contributions of LPSO phases strengthening and heterogeneous deformation-induced (HDI) strengthening led to variations in TYS in different samples. Adjusting the uniformity of the deformed grain size in the bimodal microstructure based on HDI strengthening can further enhance the synergistic improvement of the alloy's strength and ductility. [ABSTRACT FROM AUTHOR]

The rotating backward extrusion (RBE), as a novel severe plastic deformation process, has prosperous industrial application prospect. However, the capability and potential of the RBE process to prepare samples with different heterogeneous microstructures has not attracted attention. In order to explore the relationship between different microstructural compositions and mechanical properties of tubular component prepared by RBE process, the grain size distribution, grain orientation and mechanical properties of a ZK61 Mg alloy tubular component prepared by the RBE process in different regions (along the wall thickness and height directions) were investigated. The results show that the microstructure evolution in different regions is closely related to the equivalent strain distribution. The grain refinement effect is positively correlated with the equivalent strain, but a higher applied strain also leads to a strong basal orientation and high residual stress. Furthermore, the tensile deformation behavior of different samples revealed that samples with preferentially microstructural compositions (volume fraction of fine grains: 40∼60%) have better work hardening capability and strong-toughness synergy. This is mainly attributed to more effective coordinated deformation between different regions (fine grain region and coarse grain region), which can relieve local stress concentration and accommodate more dislocations. In contrast, an excessively high volume fraction of fine grains in samples limits their ability to store dislocations that saturate rapidly with increasing strain, while an excessively low volume fraction of fine grains in samples has difficulty accommodating the high density dislocations transferred from the coarse grain region, resulting in accumulation of high local stress at the interfaces of different regions (fine grain region and coarse grain region). Both of the above can deteriorate the work hardening ability and comprehensive performance, causing the sample to fail before sufficient work hardening occurs. • Microstructure distribution and mechanical properties evolution of the whole RBE ZK61 alloy tubular were revealed. • The samples with the preferred heterogeneous microstructure have the most excellent strength-toughness synergy. • The tensile deformation behavior of samples with different microstructural components was revealed. • The dominant role of fine grain region and coarse grain region in different samples was revealed. [ABSTRACT FROM AUTHOR]

• A new deformation method of RFE was proposed. • RFE can increase strain and significantly refine grains compared with FE method. • Microstructure and texture evolution of N = 0 and N = 100 were studied for comparison. This study proposed an effective plastic deformation technique, rotating forward extrusion (RFE) for producing rare-earth (RE) Mg alloy bars. The results showed that the equivalent strain increased significantly and the equivalent stress continuously decreased with increasing rotation revolutions. The metal streamline of the edge of the sample was along the extrusion direction (ED), and the center part was perpendicular to the ED. The grains were obviously refined, complete dynamic recrystallization (DRX) behavior was achieved, and the basal texture was weakened with increasing rotation revolutions during the RFE process. [ABSTRACT FROM AUTHOR]

• Loads and water content are correlated to the permanent deformation behavior of volcanic ash. • The permanent deformation of volcanic ash are predicted by prediction models. • The accuracy of the prediction models is validated using 10 sets of experiments. • Improved methods of volcanic ash are proposed. The objective of this study is to determine the deformation characteristics and prediction methods of volcanic ash in pavement ME design. For this purpose, the chemical composition, physical properties and mechanical properties of volcanic ash have been investigated. The results show that volcanic ash is an unbound fine-grained material with a maximum particle size of<2 mm, dominated by quartz, feldspar, magnetite, hematite. In this paper, repeated load triaxial (RLT) tests are conducted on 100 volcanic ash cylindrical specimens. Shakedown theory has been applied to evaluate the plastic deformation characteristics of volcanic ash, and a new criterion has been proposed to determine the shakedown boundaries of volcanic ash. The mechanistic-empirical design guide (MEPDG) model is used to determine the permanent deformation properties of the volcanic ash based on the measured permanent strain curves. Prediction models for permanent deformation properties are proposed, which consider water content, confining pressure and dynamic loads. To verify the accuracy of the prediction models proposed in this study, 10 sets of validation tests are conducted on volcanic ash specimens. The results show that the prediction models have good prediction accuracy for specimens in Rang A and Rang B under the new criterion, and poor prediction for specimens in Rang C state. However, it is important to avoid using materials in the Rang C state. Therefore, the prediction models proposed in this study can be applied to the prediction of deformation for volcanic ash pavement materials. [ABSTRACT FROM AUTHOR]