Yield Asymmetry Research Articles

Formation of gradient microstructure and elimination of tension-compression yield asymmetry of the extruded Mg-4.58Zn-2.6Gd-0.18Zr alloy via free-end torsion

Evident tension-compression yield asymmetry limited the potential use of the extruded Mg-4.58Zn-2.6Gd-0.18Zr alloy as a structural material. Pre-torsion deformation (free-end torsion) was conducted on the extruded alloy and its effects on microstructure and tensile-compressive mechanical properties were investigated in this study. It was found that the as-extruded alloy exhibited homogenous microstructure and <100>−<110 > double-peak fiber texture. Gradient structures along the radial direction were formed after pre-torsion, which contained gradient distribution of dislocations, grain size, {102} extension twin lamellas and texture components. <100>−<110 > double-peak fiber texture was gradually weakened with the torsional angle increasing from 90° to 135° and 180°, and it was related with the re-orientation of extension twinning and dislocation movement. Moreover, extension twinning was more easily to be activated in grains with <110> fiber texture component, and this phenomenon was revealed by calculating the global Schmid factor of extension twinning under pure shear stress state. Tensile and compressive yield strength increased monotonically with the increasing torsional angle. Meanwhile, ductility almost remained unchanged. Tension-compression yield asymmetry was gradually reduced, and it was eliminated after 180° pre-torsion, which was attributed to the texture weakening. The studying provided a promising and cost-effective method to enhance yield strength and reduce tension-compression yield asymmetry while also keep ductility for extruded Mg alloys.

Molecular dynamics simulation of tension and compression deformation behavior in CoCrCuFeNi high-entropy alloy: Effects of temperature and orientation

This study utilizes molecular dynamics (MD) simulations to investigate the uniaxial tensile and compressive deformation behavior of the face-centered cubic (FCC) CoCrCuFeNi high-entropy alloy (HEA) with varying orientations at different temperatures. The results indicate that the material experiences temperature-induced softening in all simulation cases. In addition, it has been observed that the mechanical properties of the CoCrCuFeNi HEA exhibit orientation dependence and tension-compression asymmetry. Analysis of the Schmid factor of the leading and trailing partial dislocations suggests that the yield asymmetry is contingent upon the leading Schmid factor asymmetry. Microstructure evolution analysis and quantitative statistics of deformation defects indicate that the plastic deformation mechanisms of uniaxial tensile deformation along the [001], [111], and [112] orientations and compressive deformation along the [110], [111], and [112] orientations can be characterized by the formation and annihilation of intrinsic stacking fault (ISF), extrinsic stacking fault (ESF), and a few twins resulting from the gliding of Shockley partial dislocations. Twins play a crucial role in compression along the [001] direction and tension along the [110] direction due to the proliferation of twin boundaries (TBs)-assisted dislocations. The interactions between stacking faults (SF) and abundant TBs cause an increase in dislocation density in the later stage of plastic deformation in the aforementioned models. A comparison with low-entropy materials and theoretical calculations reveals that alloying reduces the stacking fault energy (SFE) of the CoCrCuFeNi crystal and enhances its twinnability.

Investigation of microstructure and mechanical properties of ZK60 magnesium alloy achieved by extrusion-shearing process

The microstructure characterization, mechanical properties and texture evolution of a ZK60 alloy achieved via the extrusion-shearing (ES) process were systematically studied with the help of optical microscopy (OM), X-ray diffractometry (XRD), scanning electron microscope (SEM) and electron back-scattered diffraction (EBSD). The results showed that the grain size was refined to ∼1.7 μm and the microstructure became more uniform. The tensile yield strength and ultimate tensile strength at room temperature of the ES-processed alloy reached 263 MPa and 321 MPa, respectively, which were 35.6% and 10.7% higher than that of the as-annealed alloy. Grain refinement, precipitate strengthening, and dislocation strengthening are the main factors for the improvement in strength. After the ES process, the elongation of ZK60 alloy increased from 16.6% to 23.7%, which is attributed to the activation of the basal slip system and texture modification. Moreover, the tension-compression yield asymmetry of the ZK60 alloy was significantly improved after extrusion, thus indicating that the extrusion-shearing process suggested in this work has great potential for the large-scale application of magnesium alloys.

Formation of nanocrystalline AZ31B Mg alloys via cryogenic rotary swaging

A bulk nanocrystalline AZ31B Mg alloy with extraordinarily high strength was prepared via cryogenic rotary swaging in this study. The obtained alloy shows finer grains, higher strength, and a negligible tension-compression yield asymmetry, compared with that prepared via room-temperature rotary swaging. Transmission electron microscopy investigations showed that at the initial stage, multiple twins, mostly tension twins, were activated and intersected with each other, thereby refining the coarse grains into a fine lamellar structure. Then, two types of nanoscale subgrains were generated with increasing swaging strain. The first type of nanoscale subgrain contained twin boundaries and low-angle grain boundaries. This type of subgrain appeared at the twin-twin intersections and was mainly driven by high local stress. The second type of nanoscale subgrain was formed within the twin lamellae. The boundaries of this type of subgrain did not contain twin boundaries and were transformed from massive dislocation arrays. Finally, randomly oriented nanograins were obtained via dynamic recrystallization, under the combined function of deformation heat and increased stored energy. Compared with room-temperature rotary swaging, cryogenic rotary swaging exhibits a slower grain refinement process but a remarkably enhanced grain refinement effect after the same five-pass swaging.

Development of sustainable novel Mg-Ca-Sc alloys with exceptional corrosion resistance

Mg-based alloys have been widely researched for biomaterial and structural applications as they fulfill several prerequisites, such as lightweight, high specific strength, and good biocompatibility, which are highly desirable. However, a long-standing obstacle to the widespread use of magnesium is its low corrosion resistance and increased cost upon increasing alloying content to enhance corrosion resistance. In this study, we report the effect of the simultaneous addition of rare-earth element (Sc) and non-rare earth element (Ca) maintaining low alloying content (∼ 1 wt%) on the mechanical, tribological, and corrosion behavior of Mg. The novel as-cast Mg-0.6Ca-0.5Sc alloy exhibited excellent corrosion resistance with a corrosion rate ∼ 40 % lower than the conventional as-cast WE43 alloy and ∼ 88 % lower than AZ31 alloy. A finer grain size and strong basal texture were achieved through thermomechanical processing, further enhancing the corrosion resistance of the as-cast novel alloys by ∼ 45 %. Stress corrosion cracking and wear testing in physiological saline solution were also conducted to study the combined effect of stress and corrosive electrolyte. The tensile and compression behavior remained practically the same upon adding Sc. However, the addition of 0.5 wt% Sc reduced the yield asymmetry by ∼ 10 % in as-cast and ∼ 5 % in recrystallized conditions. Furthermore, Mg-0.6Ca-0.5Sc alloy exhibited significant strength (∼ 175 %) and ductility (∼ 67 %) improvement under tensile testing in a physiological saline solution environment compared to Mg-0.6Ca alloy. The developed novel Mg-0.6Ca-0.5Sc ternary alloy exhibited enhanced resistance to corrosion, stress corrosion cracking, and wear relative to the Mg-0.6Ca binary alloy.

A high temperature manufacturability study of ultrafine grained Magnesium Rare-Earth alloy using processing map and constitutive analysis

The rare-earth (RE) contained ultrafine grained (UFG) Magnesium (Mg) alloys are excellent materials for aerospace and automobile industries due to their ultra-light weight, high strength, reduced tension to compression yield asymmetry, etc. Despite their excellent properties, the manufacturing potential of UFG Mg-RE alloys is yet to be realized. The present work is focused on engineering UFG microstructure in a Mg-Ag-Nd alloy (a Mg-RE alloy) and establishing the manufacturing potential of such engineered UFG Mg-RE alloy via processing map and constitutive analysis studies. The processing map is developed for a temperature range of 300 °C-450 °C and a strain rate range of 0.001 s−1-1 s−1, respectively. Three stability domains and one instability domain were identified. The governing mechanisms and scientific know-how of both types of domains are established via mechanical testing followed by detailed microstructural characterization, including Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM) analysis. A unique unexplored grain boundary sliding (GBS) mechanism-based stability domain is found as a dominant mode of deformation in one of the stability domains in the engineered UFG Mg-RE alloys.

A three-dimensional constitutive model for shape memory alloy considering transformation-induced plasticity, two-way shape memory effect, plastic yield and tension-compression asymmetry

In this paper, a three-dimensional phenomenological constitutive model for shape memory alloys (SMA) is proposed with consideration given to various thermomechanical mechanisms. This model includes, for the first time in literature, the major mechanisms influencing the behaviors of SMA actuators in a unified thermodynamics framework: transformation-induced plasticity (TRIP), two-way shape memory effect (TWSME), plastic yield as well as tension-compression asymmetry. Furthermore, a new method to address the characteristics of transformation strain varying with stress levels was proposed. Moreover, a new transformation hardening function was proposed which can give a more accurate prediction of the transformation process. The three-dimensional constitutive model is solved using return mapping algorithm for an increment in a material point in the form of strain and temperature increment. The complete algorithm is proposed and the user-defined material subroutine (UMATs) for finite element problem is established. To validate the proposed SMA constitutive model, the parameters of the SMA material are determined through uniaxial tensile tests. The SMA tubes of the same material are used to conduct both experiments and simulation, with tension-compression asymmetry considered. Training experiments and simulations have been carried out on the SMA tubes, with evident TWSME observed. The typical loading conditions to trigger simultaneous transformation and plastic yield were designed, with experiments and simulations performed. According to the results, the SMA constitutive model is effective in capturing the thermomechanical response of SMA structures under various loading conditions.

A nanophotonic interferometer

The transmission of light through sub-wavelength apertures (zero-mode waveguides, ZMW) in metal films is well-explored. It introduces both an amplitude modulation as well as a phase shift to the oscillating electromagnetic field. We propose a nanophotonic interferometer by bringing two ZMW (∼100 nm diameter) in proximity and monitoring the distribution of transmitted light in the back-focal plane of collecting microscope objective (1.3 N.A.). We demonstrate that both an asymmetry induced by the binding of a quantum dot in one of the two ZMW, as well as an asymmetry in ZMW diameter yield qualitatively similar transmission patterns. We find that the complex pattern can be quantified through a scalar measure of asymmetry along the symmetry axis of the aperture pair. In a combined experimental and computational exploration of detectors with differing ZMW diameters, we find that the scalar asymmetry is a monotonous function of the diameter difference of the two apertures, and that the scalar asymmetry measure is higher if the sample is slightly displaced from the focal plane of the collecting microscope objective. An optimization of the detector geometry determined that the maximum response is achieved at an aperture separation that is comparable to the wavelength on the exit side of the sensor. For small separations of apertures, on the order of a quarter of the wavelength and less, the signal is strongly polarization dependent, while for larger separations, on the order of the wavelength or larger, the signal becomes essentially polarization-independent.

Deformation mechanisms of dual-textured Mg-6.5Zn alloy with limited tension-compression yield asymmetry

A dual-textured wrought Mg-6.5 Zn (wt.%) alloy with limited yield asymmetry (compressive yield strength / tensile yield strength: 0.90) is reported. Approximately 80% of the grains present the standard texture of wrought Mg alloys while the grain orientation is rotated by ≈ 90º perpendicularly to the c axis in the remaining 20%. The deformation mechanisms responsible for this behavior are analyzed on samples deformed in tension and compression up to different strains. Compressive deformation of the grains with the standard texture is accommodated by 〈a〉 basal slip and extension twinning while tensile deformation promotes 〈a〉 basal and non-basal 〈a〉 prismatic and 〈a〉 pyramidal slip, leading to the typical yield asymmetry. However, the rotated grains present the opposite (and much stronger) yield asymmetry because tensile deformation is absorbed by 〈a〉 basal slip and extension twinning while compression deformation requires 〈a〉 basal slip and compression twinning. Thus, the contribution of the 20% rotated grains to the overall mechanical behavior leads to (almost) similar values of the yield strength in tension and compression. This work provides a physical understanding of the deformation behavior of dual-textured Mg alloys, that can be used to develop novel dual-textured Mg alloys with limited yield asymmetry.

The microstructure and anisotropic deformation behavior of rapidly solidified ribbon consolidated Mg-Zn-X (X = Y, Gd, Nd) alloys

The paper describes the effect of the alloying elements (Y, Gd, and Nd) on the microstructure and resulting anisotropy of mechanical properties of Mg-Zn-based alloys prepared by the rapidly solidified ribbon consolidation technique. Material processing leads to the formation of a microstructure consisting of ultrafine dynamically recrystallized (DRX) α-Mg grains and worked non-DRX grains. In general, the small average grain size and overall weak texture, caused by the random orientation of small DRX grains, resulted in relatively high yield strength and moderate elongation during both tensile and compressive loading. Moreover, a reverse tension-compression yield asymmetry was achieved in the investigated alloys thanks to the microstructure features of the investigated alloys, namely the presence of different types of precipitates and/or cluster-arranged layers (CALs) of solute atoms-rich stacking faults in the α-Mg matrix.

Exploring the hadronic phase of relativistic heavy-ion collisions with resonances in ALICE

Hadronic resonances, having short lifetimes, are useful for studying the hadrongas phase that characterizes the late-stage evolution of high-energy nuclear collisions. Indeed, regeneration and rescattering processes occurring in the hadron gas modify the measured yields of hadronic resonances and can be studied by measuring resonance yields as a function of system size and comparing them to model predictions with and without hadronic interactions. Measurements of the differential yields of resonances with different lifetime, mass, quark content, and quantum numbers help in understanding particle production mechanisms, the lifetime of the hadronic phase, strangeness production, parton energy loss, rapidity yield asymmetry, and collective effects. With its excellent tracking and particle identification capabilities, the ALICE experiment measured a comprehensive set of mesonic and baryonic resonances. We present recent results on resonance production in pp, p–Pb, Xe–Xe and Pb–Pb collisions at various center-of-mass energies, highlighting new results of K*±, Λ(1520), and Σ*±(1385). The results are also compared to lower energy measurements and model calculations.

Microstructures, mechanical properties, corrosion, and biocompatibility of extruded Mg-Zr-Sr-Ho alloys for biodegradable implant applications

In this study, the microstructures, mechanical properties, corrosion behaviors, and biocompatibility of extruded magnesium-zirconium-strontium-holmium (Mg–Zr–Sr–Ho) alloys were comprehensively investigated. The effect of different concentrations of Ho on the microstructural characteristics, tensile and compressive properties, corrosion resistance, and biocompatibility were investigated. The microstructures of the extruded Mg-1Zr-0.5Sr-xHo (x = 0.5, 1.5, and 4 wt.%) alloys consisted of α-Mg matrix, fine α‒Zr particles, and intermetallic phase particles of Mg17Sr2 and Ho2Mg mainly distributed at the grain boundaries. Extensive {101¯2} tensile twins were observed in the partially recrystallized samples of Mg-1Zr-0.5Sr-0.5Ho and Mg-1Zr-0.5Sr-1.5Ho. Further addition of Ho to 4 wt.% resulted in a complete recrystallization due to activation of the particle stimulated nucleation around the Mg17Sr2 particles. The evolution of a rare earth (RE) texture was observed with the Ho addition, which resulted in the weakened basal and prismatic textures. Furthermore, a drastic increase of 200% in tensile elongation and 89% in compressive strain was observed with Ho addition increased from 0.5 to 4 wt%, respectively. The tension–compression yield asymmetry was significantly decreased from 0.62 for Mg-1Zr-0.5Sr-0.5Ho to 0.98 for Mg-1Zr-0.5Sr-4Ho due to the weakening of textures. Corrosion analysis of the extruded Mg–Zr–Sr–Ho alloys revealed the presence of pitting corrosion. A minimum corrosion rate of 4.98 mm y−1 was observed in Mg-1Zr-0.5Sr-0.5Ho alloy. The enhanced corrosion resistance is observed due to the presence of Ho2O3 in the surface film which reduced galvanic effect. The formation of a stabilized surface film due to the Ho2O3 was confirmed through the electrical impedance spectroscopy and XPS analysis. An in vitro cytotoxicity assessment revealed good biocompatibility and cell adhesion in relation to SaOS2 cells.

A synergetic approach to nullify tension to compression yield asymmetry of Mg matrix composite by in-situ TiB2 reinforcement and microstructural modification

Designing heterogeneous microstructure is a promising way to overcome the tensile/compressive yield asymmetry in light weight Magnesium metal matrix composites (Mg MMCs) for load bearing capabilities. Herein, we have adopted an innovative strategy to engineer TiB2 reinforced ZE41 matrix composite with varying microstructural features, including uniformly dispersed sub-micron sized in-situ TiB2 reinforcements, β-phase, rare-earth content T precipitates and equiaxed grain structures. This leads to prominent strength and ductility with negligible yield asymmetry in TiB2/ZE41 (1.06) as compared to unreinforced ZE41(1.38). The suppression of {10–12} extension twinning mode of deformation due to the back stress imposed by the simultaneous action of in-situ TiB2 particles and precipitates almost nullifies the yield asymmetry in TiB2/ZE41 composite. Further, the scientific knowhow on yield asymmetry behavior of ZE41 Mg alloy with/without in-situ TiB2 particles and precipitates have been established via understanding the dominant twinning mechanism, strain hardening behavior under tension and compression, Schmid factor, and {10–12} twinning interaction with particles and/or precipitates.

The effects of microstructural parameters on the tension-compression mechanical behavior of extruded Mg-XY rods using crystal plasticity finite element modeling

In the present study, the effects of rare earth element Y, texture intensity, and grain size on the tension-compression mechanical behavior of extruded Mg-XY(X = 0–3, wt pct) rods were investigated using improved phenomenological crystal plasticity. To this end, finite element modeling of a three-dimensional representative volume element (3D-RVE) was employed to consider the effects of microstructural parameters. Subsequently, the computational modeling approach was validated with the experimental data to assess the reliability of predictions of the responses of a polycrystalline aggregate. Afterward, the validated computational modeling was employed to predict the mechanical behaviors of extruded Mg-XY (X = 0–3, wt pct) by considering the role of slip/twinning activities during deformation. The results showed that the Y addition significantly improved the yield strength, ultimate strength, and ductility. Examination of the deformation modes activities indicated that the basal slip activity of extruded Mg-XY (X = 1–3, wt pct) is higher than that of extruded pure Mg due to the formation of non-basal texture components, which hindered the twinning activation. Increasing the Y content further reduced the suppression of tensile twinning activity. Therefore, the weak tension–compression yield asymmetry of extruded Mg-XY (X = 1–3, wt pct) was mainly attributed to the reduced tensile twinning activity. The simulated stress-strain curves illustrated that texture weakening, and grain refining improved the mechanical behavior and reduced tension-compression yield asymmetry.

Underlying mechanisms of variation in yield asymmetry and strain hardening behavior of extruded pure Mg with Gd addition

Effects of Gd addition on the strain hardening behavior and yield asymmetry of pure Mg are investigated by subjecting extruded pure Mg, Mg–5Gd, and Mg–15Gd (all in wt%) to tension and compression tests along the extrusion direction (ED). As the amount of Gd added to pure Mg increases, the basal texture tilts toward the ED and the distribution of c-axes of grains becomes randomized. Under tension, the strain hardening rates of all the materials decrease until fracture. However, under compression, the strain hardening rate increases in the early stage of deformation in pure Mg and Mg–5Gd, whereas it continuously decreases in Mg–15Gd. Pure Mg exhibits considerably high tension-compression yield asymmetry, with a compressive yield strength (CYS) to tensile yield strength (TYS) ratio of 0.4. In contrast, Mg–5Gd exhibits excellent yield symmetry with CYS/TYS of 0.9 and Mg–15Gd exhibits reversed yield asymmetry with CYS/TYS of 1.2. Underlying mechanisms of these drastically different Gd-addition-induced deformation behaviors of the materials are discussed in terms of the crystallographic distribution of grains and the relative activation stresses of basal slip, prismatic slip, pyramidal slip, and {10–12} twinning under tension and compression.

Controlling grain size and texture in Mg–Zn–Mn alloys from the interaction of recrystallization and precipitation

The recrystallization behavior of extruded Mg–Zn–Mn alloys was systematically investigated under different aging treatment prior to extrusion. Electron backscattered diffraction analysis was used to explore the recrystallization mechanism and corresponding effects on the basal texture of alloys during extrusion. The results show that the primary coarse particles can effectively promote recrystallization nucleation. Moreover, the precipitation of nanoscale particles during the aging process play a role in pinning the grain boundaries. Therefore, after peak-aged treatment (16 h), the extruded Mg alloy obtains uniform and fine microstructure, showing good mechanical properties: the tensile yield strength, tensile strength, elongation, compressive yield strength, and tension-compression yield asymmetry were 298 MPa, 363 MPa, 26%, 260 MPa, and 0.87, respectively.

Orthotropic Behavior of Twin-Roll-Cast and Hot-Rolled Magnesium ZAX210 Sheet.

Magnesium sheet metal alloys offer a deformation asymmetry, which is strongly related to grain size and texture. In order to predict deformation behavior as well as to provide methods to eliminate anisotropy and yield asymmetry, a lot of effort is invested in studying the tension–compression asymmetry of magnesium alloys. However, only a few studies deal with the characterization of the yield asymmetry of magnesium wrought alloys, especially Ca-containing alloys, related to temperature and strain. In this study, the orthotropic behavior of a twin-roll-cast, homogenized, rolled and finish-annealed Mg-2Zn-1Al-0.3Ca (ZAX210) magnesium alloy was investigated by tensile testing at room temperature, 150 °C and 250 °C. The r-values were determined and the Hill’48 yield criterion was used for the constitutive formulation of the plastic yielding and deformation. The yield loci calculated using Mises and Hill’48 as well as the determined r-values reveal an almost isotropic behavior of the ZAX210 alloy. The r-value increases with increasing logarithmic strain. At 0.16 logarithmic strain the r-values at room temperature vary between 1 (0°) and 1.5 (45° and 90°). At higher temperatures (250 °C), r-values close to 1 at all tested directions are attained. The enhanced yield asymmetry can be attributed to the weaker basal texture that arises during hot rolling and final annealing of the twin-roll-cast ZAX210 magnesium alloy. In comparison to AZ31, the ZAX210 alloy shows a yield behavior close to transversal isotropy. Finally, responsible mechanisms for this behavior are discussed.

Enhancing mechanical properties of Mg-Gd-Y-Zn alloys via microalloying with Ce and La

This study investigated the microstructure and mechanical properties of Mg-1Gd-1Y-1Zn (at.%) alloys containing designed amounts of Ce or La. The Mg&lt;sub&gt;5&lt;/sub&gt;(Gd,Zn) phase formed in the as-cast Mg-Gd-Y-Zn-Ce/La alloys and disappeared after a homogenization treatment at 500°C for 24 h. The addition of Ce and La resulted in the formation of Ce(Mg,Zn)&lt;sub&gt;12&lt;/sub&gt; and La(Mg,Zn)&lt;sub&gt;12&lt;/sub&gt; phases, respectively. Except for that, the Ce or La addition had no significant effect on the morphology, volume fraction, and type of the long-period stacking ordered (LPSO) phases in the Mg-Gd-Y-Zn alloy. The grain size decreased with increasing microalloying content because the heavy Ce and La atoms impeded atomic migration across the boundaries. The solute drag effect led to the formation of the rare earth texture in the extruded Mg-Gd-Y-Zn-Ce/La alloys, whose extent decreased with increasing microalloying content. The mechanical strength was improved by the addition of Ce or La at the sacrifice of ductility. In particular, La exhibited a stronger reinforcement ability than Ce when it was added to the Mg-Gd-Y-Zn alloys. Among the investigated chemical compositions, the Mg-1Gd-1Y-1Zn-0.3La alloy exhibited the highest strength because it had the finest grains, the highest volume fraction of the second phase, and the weakest texture intensity. Furthermore, the alloys showed an unusual yield asymmetry due to the difference in the deformation mode of the LPSO phase.

A crystal plasticity based approach to establish role of grain size and crystallographic texture in the Tension–Compression yield asymmetry and strain hardening behavior of a Magnesium–Silver–Rare Earth alloy

Existence of tension – compression yield asymmetry is a serious limitation to the load bearing capablities of Magnesium alloys in a number of light weight structural applications. The present work is aimed at nullifying the tension to compression asymmetry problem and strain hardening anomalies in a Magnesium – Silver – Rare Earth alloy by engineering different levels of microstructural conditions via friction stir processing and post process annealing. The existence and extent of yield asymmetry ratio in the range of microstructural conditions was experimentally obtained through quasistatic tensile and compression tests. The yield asymmetry problem was profoundly present in specimens of coarse grained microstructures when compared to their fine grained and ultra fine grained counterparts. The impact of the microstructure and associated mechanisms of plasticity on the macroscopic strain hardening behavior was established by Kock – Mecking's analysis. Crystal plasticity simulations using Viscoplastic Self Consistency approach revealed the consequential role of extension twinning mechanism for the existence of yield asymmetry and anomalies in strain hardening behavior. This was especially dominant with coarsening of grain size. Electron Microscopy and characterization were conducted thoroughly in partially deformed specimens to confirm the predictions of the above simulations. The role of crystallographic texture for inducing the polarity to Tension – Compression yield asymmetry was corroborated. A critical grain size in Magnesium – Silver – Rare earth alloy was hereby established which could nullify influences of extension twinning in yield asymmetry ratio.

Simultaneous improvement in strength and ductility of extruded Mg alloy via novel closed forging extrusion

A novel continuous plastic process employed on AZ31 Mg alloy called closed forging extrusion (CFE) was presented. The optical microscopy, scanning electron microscopy, electron back-scatter diffraction and tensile and compressive tests were employed to investigate the microstructure evolution and strengthening mechanism. The results indicated that the CFE-process can promote dynamic recrystallization (DRX), eliminate the coarsen unDRXed grain regions, refine the grains effectively, and improve the strength, plasticity and anisotropy of the alloy. The grain refinement was mainly attributed to the stress, which facilitated the nucleation of recrystallization and refined the microstructure via the CFE. The fully DRXed ultrafine grained structure improved the strength and plasticity simultaneously. After 60 s closed forging and continuous extrusion, the alloy exhibits relatively high TYS, UTS, CYS, elongation and yield asymmetry of 305 MPa, 337 MPa, 295 MPa, 27% and 0.97, respectively.