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This paper provided an effective method to further improve the mechanical properties of the AZ80+0.4%Ce magnesium alloy wheel spoke. The effect of high strength and ductility was obtained with a yield strength of 295.36 MPa, an elongation of 10%, by the combination of pre-deformation (7% deformation) and two-stage aging treatment (120 °C/9 h + 175 °C/24 h). The evolution of the microstructure and properties of the alloy was explored under the coupling conditions of different pre-deformation degrees and multi-stage aging. The results show that, pre-deformation introduced a large number of (10 1 ¯ 2) tensile twinning and dislocations, which greatly promoted the probability of continuous precipitates (CPs) appearing. On the contrary, the discontinuous precipitates (DPs) were limited by the vertical and horizontal twin structure. As a result, the pre-nucleation method of two-stage aging increased the proportion of CPs by 34%-38%. Owing to the DPs was effectively suppressed, the alloy's yield strength has been greatly improved. Besides, under multi-stage aging, the twin boundaries induce protruding nucleation to form static recrystallization by hindering the migration of dislocations, and the matrix swallows the twins, then the texture gradually tilts from the two poles to the basal plane. As an important supplement, the grain refinement and oblique texture promoted the improvement of the yield strength of the component. [ABSTRACT FROM AUTHOR]

The exploration of the relationship between process parameters and grain evolution during the thermal deformation of rare-earth magnesium alloys using simulation software has significant implications for enhancing research and development efficiency and advancing the large-scale engineering application of high-performance rare-earth magnesium alloys. Through single-pass hot compression experiments, this study obtained high-temperature flow stress curves for rare-earth magnesium alloys, analyzing the variation patterns of these curves and the softening mechanism of the materials. Drawing on physical metallurgical theories, such as the evolution of dislocation density during dynamic recrystallization, recrystallization nucleation, and grain growth, the authors of this paper establish a cellular automaton model to simulate the dynamic recrystallization process by tracking the sole internal variable—the evolution of dislocation density within cells. This model was developed through the secondary development of the DEFORM-3D finite element software. The results indicate that the model established in this study accurately simulates the evolution process of grain growth during heat treatment and the dynamic recrystallization microstructure during the thermal deformation of rare-earth magnesium alloys. The simulated results align well with relevant theories and metallographic experimental results, enabling the simulation of the dynamic recrystallization microstructure and grain size prediction during the deformation process of rare-earth magnesium alloys. [ABSTRACT FROM AUTHOR]

To tackle the critical challenge concerning the disparate performance outcomes between the spoke and rim in extruded AZ80 magnesium alloy wheel hub, finite element simulation was used to optimize the shape parameters of the hollow billet and improved equivalent strain was achieved. The paper studied the microstructure evolution and mechanical property response of the alloy after the forming process. The experimental results showed that the grain sizes of the spoke and rim were 32.95 and 33.84 μm, respectively, when using the optimized shape parameters, and both of them were completely dynamically recrystallized. Although the fine grain strengthening and precipitation hardening effects were consistently obtained in both samples, a discernible distinction was revealed by the mechanical property analysis. Specifically, the yield strength (YS) and ultimate tensile strength (UTS) of the rim specimens evinced a notable 13.8 and 15.4% higher in comparison to the spoke specimens. This discrepancy was further elucidated by the texture analysis, which illuminated that the spoke was distinguished by an extrusion direction–transverse direction double-peak basal texture, while the rim was marked by a normal direction–transverse direction (ND–TD) double-peak basal component after extrusion. The distinct texture patterns gave rise to varying predominant deformation mechanisms during loaded at room temperature, where the textured TD-oriented grains within the spoke unfriendly promoted the initiation of {10-12} tensile twinning at low yield stress, while both the ND and TD component within the hub manifested a markedly high activation of prismatic slip with high yield stress. The cumulative effect of these contrasting deformation pathways ultimately led to a marked contrast in the YS between the two regions. [ABSTRACT FROM AUTHOR]

Hot torsion tests for AZ80 magnesium alloy were carried out in the temperature range of 380 °C-260 °C, with a constant decreasing temperature rate of 10 °C/s in order to weaken the basal texture and refine the grains. The results indicated that the average grain sizes were refined forming gradient structure with increasing specimen radial position from center (12.2–5.4 μm), and that the initial basal texture intensity of the extruded magnesium alloy was weakened from 46.2 to 8.3. Furthermore, the extension twins (ETs) could be disintegrated from the twins forming separated twins with smaller sizes. Interestingly, ETs with the same twin variant intersecting with each other could be coalesced forming grains with similar orientation, while ETs with different twin variants were separated by twins boundaries contributing to grain refinement. Moreover, in addition to the conventional continuous dynamic recrystallized (CDRX) grains with 30˚ orientation rotated around C-axis of the parent grains, CDRXed grains with 30˚ rotation around a-axis and random rotation axis were also discerned. Besides, the CDRX evolution induced twins were also elaborated, exhibiting the complex competition between CDRX and twining. Hot torsion deformation with constant decreasing temperatures rate is an effective way of grain refinement and texture modification. [ABSTRACT FROM AUTHOR]

The extruded AZ80+0.4% Ce magnesium alloy was twisted in the temperature range of 300 - 380 °C by using a Gleeble 3500 thermal simulation test machine with a torsion unit. The deformed cylindrical specimens were cooled at a cooling rate of 10 °C/s or 0.1 °C/s, respectively, and aged at 170 °C. The microstructure analysis results showed that the grain size decreased with increasing specimen radial position from center (SRPC), and that the strong initial basal texture of the extruded magnesium alloy was weakened. Both continuous and discontinuous dynamic recrystallization mechanisms were involved in contributing to the grain refinement for all specimens investigated. And a novel extension twinning induced dynamic recrystallization mechanism was proposed for specimen deformed at 300 °C. For the specimens deformed at 300 °C and 340 °C followed by a slow cooling rate (0.1 °C/s), precipitates of various shapes (β-Mg 17 Al 12), with the dominant precipitates being on the grains boundaries, appeared on the surface section. For specimen deformed at 380 °C, lamellar precipitates (LPS) in the interiors of the grains were predominant. After aging, the LPS still dominated for specimens twisted at 380 °C; however, the LPS gradually decreased with decreasing deformation temperatures from 380 °C to 300 °C. Dynamically precipitated β, especially those decorating the grain boundaries, changed the competition pictures for the LPS and precipitates of other shapes after aging. Interestingly, LPS dominated the areas for the center section of the specimens after aging regardless of deformation temperatures. Low temperature deformation with high SRPC followed by rapid cooling rate increased the micro hardness of the alloy after aging due to refined grain, reduced precipitates size, decreased lamellar spacing as well as strain hardening. [ABSTRACT FROM AUTHOR]

• The current progress and characteristics of large-scale high-performance Mg alloy components were summarized. • The breakthrough of the key technology of large-scale Mg alloy components could be provided for help. • New SPD methods for large-scale Mg alloy components from blank preparation to forming stage were proposed. The lightweight of high-end equipment relies on high mechanical properties magnesium (Mg) alloy structural components, because it is the best way to improve equipment service performance and reduce energy consumption. This article summarizes the current progress and characteristics of large-scale high-performance Mg alloy components by analyzing the strengthening-toughening mechanisms, characteristics of plastic forming, and the preparation of large high mechanical properties forging blanks. Due to the lack of breakthroughs in the key technologies for forming large-scale Mg alloy components, their uniformity of mechanical properties and consistency are poor, the forming accuracy of components is low, and the production cost is high, which limit their engineering application and restrict the lightweight level of high-end equipment. In view of the above problems, the forming trends and research directions of large-scale and high mechanical properties Mg alloy components are proposed in this paper. It can provide help for the breakthrough of the key technology of large-scale Mg alloy components with high mechanical properties and expand the application of Mg alloy in high-end products. [ABSTRACT FROM AUTHOR]

RE-containing magnesium alloys were prepared via molten-salt-mediated magnesiothermic reduction by using RE 2 O 3 (RE=Y, Nd and Gd) and Mg metal as raw materials. The thermomechanical analysis of the magnesiothermic reduction reactions in molten salt was investigated. Then the molten-salt-mediated magnesiothermic reduction process was studied from three different perspectives. After that, the RE-containing magnesium alloy was characterized by using chemical analysis, XRD analysis and SEM analysis. The magnesiothermic reduction was a liquid-liquid reaction with relatively weak driving force. During the melting process and the magnesiothermic reduction process, magnesium metal and the obtained alloy went up and down as a whole in molten salt, which improved the process safety without introducing chloride inclusions. Meanwhile, the hydrolysis of the RECl 3 -containing molten salt occurred at elevated temperature, which severely impeded the magnesiothermic reduction process. After the magnesiothermic reduction at 750 °C for 2.0 h, the content of RE and the common impurity elements in the obtained RE-containing alloy met the both requirements of the commercial WE43A and WE43B. [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]

A new approach that was designed to prepare Mg–Nd binary alloys via molten-salt-mediated magnesiothermic reduction by using Nd2O3 and Mg metal as raw materials was presented. The overall approach was based on a chemical pathway that synergistically integrated a series of simple steps to produce Mg–Nd alloys that could meet the requirement of Nd content in commercial Nd-containing magnesium alloys. The key steps included preparation of NdCl3-containing molten salt, the reduction of NdCl3 by Mg in molten salt, and the removal of MgCl2 from molten salt. The results showed that this approach could indeed prepare Mg–(6 to 18) weight percent Nd binary alloys, and the remaining molten salt could be recycled after being treated with NdF3. When other parameters were fixed, the Nd content in alloy could be adjusted only by adjusting the concentration of NdCl3 and MgCl2 in molten salt. Besides, a decrease in temperature or an increase in the mass ratio of molten salt to Mg could further increase the Nd content in alloy when other conditions were fixed. [ABSTRACT FROM AUTHOR]

In the present work, two processing routes (A and B) with 3 CEE-AEC passes are performed on Mg–13Gd–4Y–2Zn–0.4Zr alloys, and the resultant microstructure evolution, texture analysis and mechanical properties are investigated systematically. The core difference between the two processing routes is the orientation between the expansion and extrusion steps, i.e., they are parallel to each other for on route A and perpendicular to each other for route B. The results show that a remarkable grain refinement is achieved via both processing routes due to dynamic recrystallization (DRX). Fine equiaxed grains are observed in the samples processed with route B with a final size of 3.6 ± 0.4 µm compared to the grain size of 4.5 ± 0.5 µm with route A. With an increasing number of CEE-AEC passes, the overall texture intensity decreases, and the basal texture gradually changes to the mixed texture components. The shear deformation introduced by the asymmetrical extrusion cavity promotes a broad angular distribution of the basal planes on routes A and B, leading to an obvious increase in the Schmid factor for the activation of the basal 〈a〉 slip system. The tensile test at ambient temperature reveals that the comprehensive mechanical properties are improved, and the conventional mechanical anisotropy of as-received alloys is alleviated by successive CEE-AEC processing, which is mainly derived from the competitive balance relation between the grain refinement and texture modification. [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]

To solve the difficulties associated with integral precise extrusion forming for complex components of magnesium alloy, Deform-3D finite element simulation software was used to conduct numerical analyses for the forming process. Different extrusion schemes were used for determining the overall extrusion difficulties associated with special-shaped thin-walled complex components of magnesium alloy. The effects of a preformed blank on the filling and formation of folding defects in the forming process were studied. Based on the principle of minimum energy in the process of plastic deformation and the law of least resistance, volume predistribution and equal distance flow quantitative compensation methods were put forward. These methods were used to optimize the size and structure of the preform, forming a uniform material flow distribution. They also enabled one to manifest a uniform material flow velocity distribution, reduce the forming load, and avoid the creation of folding and filling defects during the final forming, for the realization of an efficient and reliable preform optimization design for magnesium alloy profiled complex components. The results obtained from a forming test, microstructure and mechanical properties test showed that the mechanical properties of the extruded component all met the service indexes. This design method can provide a theoretical reference for preforming design of profiled complex components. [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]

High-purity anhydrous MgCl2-containing molten salt was directly synthesized from MgCl2 · 6H2O via complex salts dehydration and protection. After that, Mg-Al and Mg-Zn alloys were prepared by electrochemical codeposition. The hydrolysis processes of magnesium chloride hexahydrate in various chloride mixtures were studied. Then, the preparation process was studied and the dehydration mechanism was put forward. NH4Cl·MgCl2·nH2O formed under 300°C inhibits the formation of hydrolysate during the dehydration process. KMgCl3 and K3NaMgCl6 formed above 400°C can further protect the unstable anhydrous MgCl2. Therefore, high-purity anhydrous MgCl2-containing molten salt with w(MgO)/w(MgCl2) being 0.016 wt.% was obtained. The current efficiency was above 81% and 97%, respectively, when preparing Mg-Al alloys and Mg-Zn alloys, and the alloying elements were distributed homogeneously in the alloy matrix. [ABSTRACT FROM AUTHOR]

The microstructure, deformation mechanisms, dynamic recrystallization (DRX) behavior, and texture evolution of AZ80 magnesium alloy were investigated by three-pass cyclic expansion-extrusion (CEE) tests. Optical microscopy (OM), electron back-scattered diffraction (EBSD), and X-ray diffraction (XRD) were employed to study microstructure, grain orientation, DRX mechanism, and texture evolution. The results show that the grain sizes decrease continuously with the increase of CEE pass. The grain refinement effect of the first pass is the most remarkable, and there appear a large number of twins. After three-pass CEE, a well-distributed structure with fine equiaxed grains is obtained. With the increase of CEE pass, the deformation mechanism changes from twinning to slipping and the DRX mechanism changes mainly from twinning-induced dynamic recrystallization (TDRX) to rotation dynamic recrystallization (RDRX) and then to continuous dynamic recrystallization (CDRX). The grain misorientation between the new grains and matrix grains deceases gradually, and a relatively small angle misorientation is obtained after three-pass CEE. Grain misorientations of the first two passes are attributed to TDRX and RDRX behaviors, respectively. The grain refinement changes the deformation and DRX mechanisms of CEE process, which leads the (0002) basal texture intensity first decrease and then increase suddenly. Eventually, the extremely strong basal texture is formed after three-pass CEE. [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 method of backward extrusion through rotating die and open punch, named rotating backward extrusion (RBE), is proposed. In this new process, a torque is imposed on the die that drives billet rotating. The rotating billet was backward extruded with the use of the punch with end face groove. To investigate the capability of this process, the experiment and finite element (FE) analysis were carried out for AZ80 magnesium alloy used as experimental material. The effects of rotating speed on the effective strain and process load were analyzed. The effective strain of the final part and process load were compared for cup extrusion by both the conventional and the new process respectively. The results showed that the average effective strain through the processed sample was approximately higher in 3 times the value of the sample processed via the conventional backward extrusion. The reduction of process load is about 20% in maximum in comparison with the conventional backward extrusion process. This new process has proven to be promising for the hollow parts production because of lower process force and imposing higher effective strain. The potential for grain refinement and mechanical properties improvement are required to fully evaluate for the new process. [ABSTRACT FROM AUTHOR]

The hot deformation and dynamic recrystallization behaviors of as-homogenized Mg–12Gd–4.5Y–2Zn–0.4Zr alloy were investigated through compression tests in this paper. This work presents the appropriate deformation zone. Different degrees of discontinuous dynamic recrystallization occurred in the alloys under different strain rates and temperatures. The critical strain prediction model of these alloys during hot deformation was obtained through calculation of work hardening rate θ , inflection points in the l n θ − ε curves and the minimum value of the − ( ∂ ( l n θ ) / ∂ ε ) - ε curves. At lower strain rates and temperatures, kink band deformations constitute an essential mechanism for homogeneous strain creation. As the strain rate increased, the kink band deformations became significantly serious, the new kinks were formed within the former kink bands, leading to grain refinement. In addition, a low amount of discontinuous dynamic recrystallizations occurred. As the strain rate increased, the volume fraction of discontinuous dynamic recrystallization was increased, whereas the kink band deformation decreased. [ABSTRACT FROM AUTHOR]

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The flow stress behaviors of both the as-cast and homogenized Mg-8Gd-3Y-1Nd-0.5Zr alloy were investigated using a Gleeble-1500 thermal simulation test machine in the temperature range of 460-520 °C and strain rate range of 0.001-1 s. The processing maps for the two alloys were developed on the basis of flow stress data obtained at a strain of 0.5. It was found that the processing maps of both the as-cast alloy and homogenized alloy consisted of one stability and one instability domains. According to the processing maps and the microstructural observations, the optimum hot-working parameters for the two alloys were determined to be at a temperature of 500 °C and at a strain rate of 0.01 s. The hot workability of the homogenized alloy was better than the as-cast alloy in the safe domain, while the homogenization treatment increased the instability domain. The microvoids, which initiated along the dynamic recrystallized (DRX) grain boundaries and led to intercrystalline cracking, were an important factor contributing to the expanded instability domains for the homogenized alloy. Dynamic precipitation in the DRX grain in the as-cast alloy contributed to a lower DRX, hence prevented the formation of microvoids, which resulted in a reduced tendency for DRX intercrystalline cracking during hot deformation. [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 RSE process can produce more strain and more complete metal flow than BE. • The RSE process can refine the grain structure and uniformly distribute the second phases at a smaller size. • The texture strength can be effectively weakened by the RSE process. • As the RSE deformation progresses, DDRX plays a leading role. • The RSE process can expand the range of deformation effects along the TD at the same extrusion ratio. In this work, we use a kind of punch with a shear structure by combining torsion and backward extrusion (BE) to produce a ZK60 alloy cylinder part by rotating shear extrusion (RSE) at 643 K. This process can introduce a torsional shear component on the basis of backward extrusion by changing the direction of plastic flow and increasing the shear deformation amount to make it easier for the material at the bottom of the punch to flow to the barrel wall. Compared with BE, RSE can obviously refine grains and effectively improve the problems of a small deformation amount and insufficient flow of the material at the bottom of the back extrusion punch. The relevant microstructure evolutions of different parts of formed cylinder parts are investigated, and the results show that the proportions of dynamic recrystallization (DRX) in the inner and the middle wall of the lower half region of RSE processed part increase obviously (by 49% and 21.7%, respectively) and that the size of fine grain is ~2–4 µm; further, that of the bottom of the barrel increases by 44.6%. The deformation mechanisms of rotating shear are mainly continuous DRX (CDRX) accompanied by discontinuous DRX (DDRX) in the early stage, and with the progress of deformation, DDRX plays a leading role. The (0001) plane in the BE processed part is basically parallel to the transverse direction (TD), while the (0001) plane in the RSE part is deflected to the extrusion direction (ED) and at an angle of 30°−45° to the TD, and the texture strength is obviously weakened. A comparison of the variation in ∆Hv(%) along the TD of the barrel wall of the two extruded parts shows that RSE can generate a larger deformation amount and wider deformation effect range under the same extrusion ratio, effectively improving the microhardness of the ZK60 alloy. The ultimate strength (UTS), yield strength (YS), and elongation (EL) of alloy are ~313 MPa, ~279 MPa, ~12.1% after the RSE process, respectively. And the strength and ductility of the alloy can be improved by the RSE process. [ABSTRACT FROM AUTHOR]

There is a new long-period stacking ordered structure in Mg–RE–Zn magnesium alloys, namely the LPSO phase, which can effectively improve the yield strength, elongation, and corrosion resistance of Mg alloys. According to different types of Mg–RE–Zn alloy systems, two transformation modes are involved in the heat treatment transformation process. The first is the alloy without LPSO phase in the as-cast alloy, and the MgxRE phase changes to 14H-LPSO phase. The second is the alloy containing LPSO phase in the as-cast state, and the 14H-LPSO phase is obtained by the transformations of 6H, 18R, and 24R. The effects of different solution parameters on the second phase of Mg–9Gd–2Y–2Zn–0.5Zr alloy were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The precipitation mechanism of 14H-LPSO phase during solution treatment was further clarified. At a solution time of 13 h, the grain size increased rapidly initially and then decreased slightly with increasing solution temperature. The analysis of the volume fraction of the second phase and lattice constant showed that Gd and Y elements in the alloy precipitated from the matrix and formed 14H-LPSO phase after solution treatment at 490 °C for 13 h. At this time, the hardness of the alloy reached the maximum of 74.6 HV. After solution treatment at 500 °C for 13 h, the solid solution degree of the alloy increases, and the grain size and hardness of the alloy remain basically unchanged. [ABSTRACT FROM AUTHOR]

This work is to study the microstructure and texture evolution of AZ31 alloy prepared by cyclic expansion extrusion with an asymmetrical extrusion cavity (CEE-AEC) at different deformation temperatures. The result shows AZ31 alloy undergoes continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) during CEE-AEC processing. At the initial stage of deformation, AZ31 alloys exhibit similar bimodal microstructure of coarse deformed grains surrounded by fine DRXed grains. As the passes increase, the cumulative strain increases, and the coarse grains of all samples are almost replaced by fine equiaxed grains. The average grain sizes and the basal texture intensities of the deformed samples increase as the deformation temperature increases. In addition, due to the existence of an asymmetrical cavity, as the passes increase, the basal textures of all samples are deflected with maximum intensities increase, and even an unusual bimodal texture is formed, resulting in a soft orientation that is easy to basal slip. [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 study, homogenized Mg-13Gd-4Y–2Zn-0.5Zr alloys were applied to multi-directional forging (MDF) process at decreasing temperatures from 480 °C to 420 °C by 4 passes. The microstructure, texture evolution and mechanical properties of the alloys during the MDF process were investigated. The result showed that the average grain size was refined remarkably to 4.0 μm and the microstructure distribution became homogeneous after 3 passes with cumulative strain of 9. After 4 passes with cumulative strain of 12, the average grain size increases to 5.4 μm. It is observed that large number of dynamic recrystallized (DRXed) grains and spherical precipitated phases of Mg 5 (Gd,Y,Zn) occurred during the MDF processing. The area fraction of DRXed grains was increased to 97.3% that can be regarded as achieving complete dynamic recrystallization (DRX) after 3 passes. The grain refinement was mainly caused by DRX, and the DRX was induced via particle stimulation nucleation (PSN) mechanism. Moreover, part of lamellar long-period stacking ordered (LPSO) phases were kinked and brought about numerous kink bands during multi-directional forging (MDF) process, which had an important impact on the grain refinement. As the MDF passes and cumulative strain increase, the basal texture transformed from strong basal texture to a random distribution gradually. The maximum ultimate tensile strength (UTS) and tensile yield strength (TYS) were 399 MPa and 308 MPa after 3 passes. The maximum failure elongation (FE) was 18.1% after 4 passes. • Grain refinement and texture weaken could be achieved during MDF process for Mg–13Gd–4Y–2Zn–0.5Zr alloy. • Microstructure, texture evolution and mechanical properties of MDFed alloy were discussed. • The strengthening mechanism was discussed based on microstructure and texture evolution. [ABSTRACT FROM AUTHOR]

• A rotary extrusion forming process for cylindrical tubular parts is proposed. • The deformation behavior of rare-earth magnesium alloy under direct extrusion and rotary extrusion was compared. • The flow stress of the rotary extrusion is significantly lower than that of the direct backward extrusion. • The cup-shaped parts formed via rotary extrusion exhibits a typical gradient structure. • The width of refinement becomes wider as the rotations number increases. Rotary extrusion is a technique to produce workpieces with a very large strain and a weak texture. In this work, deformation behavior and microstructure evolution of magnesium alloys via rotary extrusion were investigated. The results show that the flow stress of the rotary extrusion is significantly lower than that of the direct backward extrusion. The equivalent stress decreases upon the increase of the rotations number. The cup-shaped parts formed via rotary extrusion exhibits a typical gradient structure, which expands from its center to the borders. The basal texture of the sample is smaller than that produced by direct backward extrusion. Moreover, it further decreases upon the increase of the rotation number. [ABSTRACT FROM AUTHOR]

Microstructure evolution and mechanical properties of AZ80 Mg alloy during annular channel angular extrusion (350 °C) and heat treatment with varying parameters were investigated, respectively. The results showed that dynamic recrystallization of Mg grains was developed and the dendritic eutectic β-Mg17Al12 phases formed during the solidification were broken into small β-phase particles after hot extrusion. Moreover, a weak texture with two dominant peaks formed owing to the significant grain refinement and the enhanced activation of pyramidal slip at relative high temperature. The tension tests showed that both the yield strength and ultimate tensile strength of the extruded alloy were dramatically improved owing to the joint strengthening effect of fine grain and β-phase particles as compared with the homogenized sample. The solution treatment achieved the good plasticity of the alloy resulting from the dissolution of β-phases and the development of more equiaxed grains, while the direct-aging process led to poor alloy elongation as a result of residual eutectic β-phases. After solution and aging treatment, simultaneous bonding strength and plasticity of the alloy were achieved, as a consequence of dissolution of coarse eutectic β-phases and heterogeneous precipitation of a large quantity of newly formed β-phases with both the morphologies of continuous and discontinuous precipitates. [ABSTRACT FROM AUTHOR]

The effects of repetitive upsetting extrusion under different starting temperatures on the microstructure and texture of GWZK124 alloy were investigated. The results clearly showed that the particles and second phases induced dynamic recrystallization (DRX), which can be explained by the particle-stimulated nucleation (PSN) mechanism. It was shown that grain refinement during repetitive upsetting extrusion (RUE) is dominated by a complicated combination of continuous dynamic recrystallization and discontinuous dynamic recrystallization. The RUEed alloys under different starting temperatures exhibited a bimodal microstructure comprising fine DRXed grains with weak texture and coarse deformed grains with strong texture. The DRXed grains could weaken the texture. As the RUE starting temperature decreased, the average grain size increased and the volume fraction of DRXed grains decreased. [ABSTRACT FROM AUTHOR]

Ultra-thin-walled tubes of magnesium alloys have received more and more attention in producing precision components for medical devices. Therefore, thin-walled tubes with high quality are desperately needed. In this study, the process of multi-pass variable wall thickness extrusion was carried out on an AZ80 + 0.4%Ce Mg alloy with up to five passes—one-pass backward extrusion and four-pass extension—to fabricate the seamless thin-walled tube with an inside diameter of 6.0 mm and a wall thickness of 0.6 mm. The average grain size decreased from 46.3 μm to 8.9 μm at the appropriate deformation temperature of 350 °C with the punch speed of 0.1 mm/s. X-ray diffraction (XRD), optical microscope (OM), scanning electron microscopy (SEM), and the Vickers hardness (HV) tester were utilized to study the phases, microstructure, and hardness evolution. It can be observed that low deformation temperatures (240 °C and 270 °C) and low strain (1 pass extrusion and 1 pass extension) lead to twins that occupy the grains to coordinate deformation, and a slip system was activated with the accumulation of strain. The results of the Vickers hardness test showed that twinning, precipitation of second phases, twinning dynamic recrystallization (TDRX), and work hardening were combined to change the hardness of tubes at 240 °C and 270 °C. The hardness reached 93 HV after the third pass extension without annealing at 350 °C. [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]

Repetitive upsetting extrusion (RUE) was applied to the as-homogenized Mg-12.0Gd-4.5Y-2Zn-0.4Zr (wt %) alloy at 773 K. The microstructure evolution of the alloy during RUE was investigated. The results indicated that almost all Mg5(Gd,Y,Zn) phases and fine-lamellar long-period stacking-ordered (LPSO) phases were dissolved into the matrix after homogenization treatment at 793 K for 16 h. After one RUE pass, dynamic recrystallization (DRX) occurred. During subsequent RUE passes (from one to three passes), average volume fractions of DRXed grains increased from 43.9% to 65.8%, and that of fine-lamellar and block-shaped LPSO phases gradually decreased. All samples exhibited a typical bimodal microstructure consisting of some initial grains containing fine-lamellar LPSO phases, but consisting mostly of fine-DRXed grains with a mean grain size of 6 μm. Because of an increase in the accumulated strains, the coarse grains were substituted with fine-DRXed grains, the grains were gradually refined, and the microstructure distribution became more homogeneous. [ABSTRACT FROM AUTHOR]

As a commonly used component in the aerospace and transportation industries, tubular components have received increasing attention from researchers. The rotary backward extrusion (RBE) method can efficiently form tubular components with excellent properties. However, its microstructures and properties exhibit heterogeneous characteristics in the radial direction. The equivalent strain distributions, microstructure distributions, tensile properties, and dynamic recrystallization (DRX) mechanisms of the AZ80 specimens were investigated by combining finite element simulation with physical experiments. The results showed that the equivalent strain, microstructure, and mechanical properties of the tubular sample formed by RBE were gradient distributed along the radial direction. As the rotational speed of the die increased, the gradient of the equivalent strain of the specimens increased; however, the gradient of the microstructures and mechanical properties decreased. The influence of the die motion parameters on the equivalent strain and the effects of the equivalent strain on the microstructures and mechanical properties of the specimen were revealed. Additionally, the DRX behavior of fine-grain AZ80 Mg alloy tubes produced by the RBE process includes both continuous and discontinuous DRX. This study could provide a theoretical foundation for accurately controlling the microstructure distributions of tubular parts to achieve uniform high mechanical properties. The findings are expected to promote the large-scale application of magnesium alloys in industry. [Display omitted] • A novel extrusion method for manufacturing strain-controlled tubular parts. • The dies motion parameters have significant effects on strains, microstructures, and properties of tubes. • The microstructures and mechanical properties of the tubes can be made more uniform through the rotary backward extrusion. [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]

The Mg-13Gd-4Y–2Zn-0.5Zr (wt.%) alloy containing high-content long-period stacking ordered (LPSO) phases is pre-solutioned prior to multi-directional forging (MDF) process. The microstructural evolution of the experimental alloy via MDF method after 4 passes is studied by the ways of optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and electron backscattered diffraction (EBSD), and the mechanical properties of the MDFed alloys after different passes is calibrated by vickers hardness. Unlike conventional MDF method, we perform pre-solution treatment for the MDFed alloys from 2 passes to 4 passes in order to make more precipitation phases be resolved to strengthen the Mg matrix and obtain the uniform microstructure. It is obvious to find that amount of plate-like Mg 5 RE phases are existing in the 4MDFed sample. And the occurrence of the plate-like Mg 5 RE phases is attributed to the activation of basal slip and prismatic slip under certain strain conditions in the deformation processing. • Large size and large plastic deformation on high-rare-earth magnesium alloy of homogenized Mg–13Gd–4Y–2Zn–0.5Zr alloy was studied during MDF process under high and low temperature cycle deformation condition. • The precipitation evolution was discussed based on microstructure evolution and microhardness. • The types and shapes of the precipitation phases have a certain relationship with the deformation passes and temperature. [ABSTRACT FROM AUTHOR]

Hot deformation behaviors of the extruded AZ80 + 0.4% Ce magnesium alloy plate were investigated in the temperature range of 300–420 °C and strain rate range of 0.0005–0.5 s−1 by using a Gleeble 3500 thermal simulation test machine. The cylindrical specimens for hot compression tests were cut in 0°, 45° and 90° to the extruded direction of the plate, respectively. The microstructure analysis was carried out with optical microscopy (OM), X-ray diffractometry (XRD) and scanning electronic microscopy (SEM). The results showed that the flow stresses of the 0°, 45° and 90° specimens exhibited anisotropic behaviors, which weakened with increasing temperatures, strains, and decreasing strain rates. The processing maps of different specimens were calculated and analyzed according to the dynamic materials model. The optimized stability domains for all the three specimens were in the temperature range of 380–420 °C and strain rate range of 0.0005–0.005 s−1, while the instability domains varied with specimen orientations. The apparent activation energy of the 0°, 45° and 90° specimens were 154.45 kJ/mol, 129.16 kJ/mol and 145.97 kJ/mol, respectively, suggesting the change of deformation mechanisms with specimen orientations. The operation of different slip systems, which were indicated by the varying values of the Schmid factor, should be responsible for the anisotropic hot deformation behaviors for the extruded AZ80 + 0.4%Ce magnesium alloy plate with basal texture. Image 1 • The flow stresses of the 0°, 45°and 90°specimens exhibited anisotropic behaviors, which weakened with increasing temperatures, strains, and decreasing strain rates. The processing maps of different specimens were calculated and analyzed according to dynamic materials model. • The optimized stability domains for all three specimens were in the temperature range of 380–420 °C and strain rate range of 0.0005–0.005 s-1, while the instability domains varied with specimen orientations. • The apparent activation energy of the 0°, 45°and 90° specimens were 154.45 kJ/mol, 129.16 kJ/mol and 145.97 kJ/mol, respectively, suggesting the deformation mechanisms changed with specimen orientations. • The operations of different slip systems should be responsible for the anisotropic hot deformation behaviors for the extruded alloy. [ABSTRACT FROM AUTHOR]

• Effect of the extrusion process for AZ80 wheel on fatigue has been investigated. • Link between microstructure and mechanical behaviors of AZ80 wheel was established. • Microstructure evolution in initial stage for cyclic deformation has been delivered. • The fatigue crack initiation and propagation for AZ80 magnesium alloy was studied. In order to provide a reliable theoretical foundation for fatigue resistant design of the magnesium alloy automobile wheel, specimens machined from rim and disc of the extruded AZ80 wheel were subjected to strain-controlled fatigue tests. Various characterizations (such as microstructure and texture analysis, stress-strain response monitoring, twinning/detwinning behavior evolution, and fatigue fracture morphology analysis) have been carried out to investigate the static and fatigue performance of the AZ80 wheel. The obtained microstructural analysis revealed that the rim sample exhibited finer and more homogeneous dynamic recrystallized grains with the average grain size of ~17.2 μm, while ~30.5 μm for the disc sample. The rim specimen achieved the ultimate tensile strength of ~339 MPa with a noticeable elongation to fracture of ~14.6%. In addition, the rim sample also showed superior fatigue properties as compared with the disc sample, which was related to the smaller grains and the weaker texture intensity. The twinning/detwinning behavior participated in the cyclic deformation above the strain amplitude of 0.4% for both samples, resulting in asymmetric hysteresis loops and residual twins. The fatigue crack initiation site was observed with second phase particles and secondary cracks near the surface for all specimens, and in particular, cleavage-like faceted area with twins was identified at strain amplitude of 1%. [ABSTRACT FROM AUTHOR]

The texture evolution mechanism of Mg-13.1Gd-3.9Y–2Zn-0.4Zr (wt%) alloys during reciprocating upsetting extrusion (RUE) and subsequent heat treatment were investigated in this study. The relationship between texture weakening and deformation mechanism during multi-pass deformation was further discussed. The results show that the strong (0001)∥ED basal texture was formed after RUE, which decreases with the increase of deformation passes; the texture type had no obvious change after T5 treatment, and the texture intensity decreases significantly after T6 treatment. The high proportion of deformed grains determines the formation of strong basal texture after a single pass deformation. Due to the strong anisotropy of LPSO phases, deformed grains with different initial orientations participate in deformation through kinking or activation of basal slip and prismatic slip, respectively, and have different effects on the final texture components. With the strain increases (2 P), the deformed grains are consumed by DRXed grains with random texture, and the non-basal slip of DRXed grains became the main deformation mechanism. After T6 heat treatment, the < 11 2 ̅ 0 > fiber texture components were formed in the sample, which is due to the random nucleation and preferential growth of recrystallized grain during solution treatment. The mechanical properties of the alloys are significantly improved after RUE deformation, but the improvement on ED is better than that on TD. The mechanical properties of the alloys are improved by T5 or T6 heat treatment. The anisotropy of the former is still maintained, while that of the latter is basically eliminated. • In this paper, the texture evolution mechanism of rare-earth magnesium alloys containing LPSO phases during deformation and its texture stability during subsequent heat treatment were investigated based on RUE severe plastic deformation.The relationship between texture weakening and deformation mechanism during multi-pass deformation is further explored. • The results show that the deformed grains with different initial orientations participate in the deformation through kinks and the activation of multi-slip system under the influence of the strongly anisotropic LPSO phases, and then they have different effects on the final texture components. • The DRXed grains consume the deformed grains through the DDRX and CDRX mechanisms under low and high strain, respectively, and gradually dominate the texture type with the increase of the cumulative strain. However, the orientation of DRXed grains is still very similar to the orientation of deformed grains after extrusion, reflecting a certain genetic effect. • As for the texture transformation of the alloy after subsequent heat treatment, the results show that T5 hardly changes the texture strength and type of the alloy, while the alloy after T6 treatment has a preferred orientation due to the occurrence of static recrystallization. • The mechanical properties of the alloys are significantly improved after RUE deformation, but the improvement on ED is better than that on TD. After T5 or T6 heat treatment, the mechanical properties of the alloys are further improved, the former still retains the anisotropy after deformation, and the anisotropy of the latter is almost eliminated. [ABSTRACT FROM AUTHOR]

In this paper, the fatigue behaviour and failure mechanisms of extruded AZ80 magnesium alloy samples were studied with different initial structures. The results show that the twinning-twinning behavior was inhibited to a certain extent by fine grain and precipitates, but the initiation of fatigue cracks was promoted. Studies of the fatigue life and fracture mechanism show that both residual twins and precipitated phases can cause fatigue crack initiation, but less fatigue damage is caused by the twin-induced cracks than by second phase-induced. [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]

Abstract: In this study, the microstructure evolution of AZ80 magnesium alloy, in particular the precipitation mechanism of β Mg17Al12 phase, during hot deformation at different temperatures was characterized by SEM and the effect of the morphology of the β phase on tensile properties at room temperature was investigated. It was revealed that AZ80 cast ingot exhibited a net-work microstructure with the Mg17Al12 particles precipitating mainly in the vicinity of the grain boundaries. The net-work largely remained after the homogenization treatment. Hot-compression tests were carried out under a constant compressing speed of 8mm/s in the temperature range 200–400°C and an equivalent strain range 0.80–2.65. It was found that the net-work was destroyed during hot-compression and the following Mg17Al12 morphologies were observed depending on the hot-compression temperature and strain: strip, fine granular and lamellar. Hot-deformation has significantly improved the mechanical properties of the alloy due to refinement of grain size and change of Mg17Al12 morphology from net-work to favorable fine granular shape. [Copyright &y& Elsevier]

• One pass repetitive upsetting-extrusion(RUE) apply to process AZ80 Mg bars under different deformation parameters. • A weaker fiber texture is developed via RUE of extruded bars due to the application of interactive stress state. • Deformation parameters affect microstructure evolution, acting on strength, plasticity and anisotropy of extruded bars. • The tensile yield anisotropy of extruded bars is greatly reduced due to texture dispersion and grain refinement. [Display omitted] Repetitive upsetting-extrusion (RUE) is known as a processing method that effectively improves the properties of a billet without changing its initial shape. In this paper, one pass RUE with reduced deformation temperature (re-upsetting at 360 °C and secondary extrusion at 340 °C) and different extrusion speeds (0.5 and 1 mm/s) is implemented to improve the strength and toughness of AZ80 Mg rods, and simultaneous reduction in tensile anisotropy is achieved. Influences of one pass RUE method on the resulting microstructure and texture evolution of the alloy are investigated alongside their correlated impact on its mechanical properties. After RUE processing, the grain structure of AZ80 alloy is characterized by numerous fine dynamic recrystallized (DRXed) grains, combined with large unDRXed grains obtained at high extrusion speed or coarse DRXed grain bands obtained at low extrusion speed. Besides, β-Mg 17 Al 12 particles dynamically precipitated during deformation, acting as strong barrier against grain boundary migration through pinning effect. Through introduction of an interactive stress state, the RUE process promotes dispersion of the fiber texture that typically develops during the extrusion process. The key factor that promotes weakening of the fiber texture is derived from the refinement of basal orientated deformed grains, which form during upsetting deformation, into numerous non-basal orientated DRXed grains during early-stage extrusion. Compared with coarse deformed grains, these fine DRXed grains delay transformation of texture into the typical [10-10]–[11-20] fiber component. Grain refinement is implicated as the most significant factor with respect to simultaneous improvement of strength and toughness in the extruded rods, while tensile yield anisotropy in response to loading along the ED and TD is attributed to unDRXed grains with [10-10] fiber orientation. Compared to the as-cast state, extruded rods demonstrate increases in yield strength, ultimate tension strength, and elongation maximally up to ~2.6, ~2.2, and ~4.9 times, respectively. And when complete DRX structure is nearly achieved, the tensile yield anisotropy of extruded bar is effectively eliminated because the refined grains with relatively dispersed orientation inhibit the nucleation of tension twin and simultaneous enhance the Hall-Petch effect. [ABSTRACT FROM AUTHOR]

Based on the repetitive upsetting-extrusion (RUE) process, the evolution of the LPSO phase and its effect on the dynamic recrystallization (DRX) of Mg-9Gd-4Y–2Zn-0.5Zr (wt%) alloy during the multi-pass deformation were studied. The results showed that with the increase of RUE processing, the DRX fraction gradually increased, the grains were effectively refined, and the texture was weakened. The lamellar LPSO phase mainly underwent mechanical crushing, bending, tearing, and kinking to become refinement. The block-shaped LPSO phases dissolved during the deformation process, forming a stripe-like structure, and its rest of the refinement mechanism was similar to the lamellar phase. The refinement of block-shaped phase was slower than that of lamellar phase. However, the block-shaped phases always promoted DRX through the PSN mechanism, while the lamellar phases with a large volume inhibited the generation of DRX. After the refinement of lamellar phases, the inhibition effect was transformed into the promotion effect, which leaded to a continuous increase in the DRX fraction. This further promoted the uniform distribution of the LPSO phases and obtained a more ideal microstructure. • Repetitive upsetting-extrusion and DRX refined microstructure and weakened texture. • LPSO phases mainly refined by mechanical crushing, bending, tearing, and kinking. • The block-shaped phases dissolved to a stripe-like structure, promoting refinement. • Refined lamellar phases promoted DRX while large lamellar phases inhabited DRX. [ABSTRACT FROM AUTHOR]

The repetitive upsetting-extrusion (RUE) experiments of Mg-RE-Zn alloy were carried out to study the grain refinement and texture evolution under different decreasing temperature degrees during the deformation process. The results showed that during the RUE processing, the samples underwent dynamic recrystallization (DRX) and exhibited the similar bimodal microstructure comprising coarse deformed grains and fine dynamic recrystallized grains around. The continuous dynamic recrystallization (CDRX) process and the discontinuous dynamic recrystallization (DDRX) process occurred simultaneously, promoting grain refinement. The particles and the second phases precipitated, which effectively induced DRX to occur through the particle-stimulated nucleation (PSN). As the degree of decreasing temperature and the initial deformation temperature increased, the average grain size and texture intensity of the alloy decreased because the volume fraction of DRXed grains with small grain size and weak texture increased. • RUE applied to the GWZK124 alloy under different decreasing temperature degrees. • The fraction of DRX increased as the decreasing temperature degree increased. • The particles and second phases induced DRX, which was explained by PSN. • The CDRX and DDRX effectively refined the RUEed alloy grains. • The texture intensity decreased with increasing the fraction of DRX during RUE. [ABSTRACT FROM AUTHOR]