Extruded Magnesium Alloy Research Articles

Optimization in strength-ductility synergy of extruded Mg-3Sn-2Al-1Zn-0.6Y-0.6Nd alloy via novel FPE processes

Three novel FPE processes were proposed by integrating the advantages of conventional extrusion and ECAE, optimizing the strength-ductility synergy of extruded Mg-3Sn-2Al-1Zn-0.6Y-0.6Nd alloy. The deformation mechanism, evolution of texture and variation of the tensile properties of the alloy were investigated. Findings indicate that the alloys fabricated by the FPE processes exhibit a finer and more uniform microstructure with the lowest dislocation density, undergoing the most complete DRX. The FPE process breaks the strength-ductility tradeoff dilemma of the magnesium alloys, achieving a synergistic enhancement of both strength and ductility. The FPE-105 process was determined to be the best process for strengthening the alloy, with a 24.4 % (340 MPa) increase in UTS compared to the FE-10 sample, along with an impressive doubling of the ductility (18.6 %). The excellent mechanical properties provided by the FPE-105 process are primarily stem from the uniform and fine grain distribution and texture modification. The successful application of the three FPE processes to the fabrication of extruded magnesium alloys demonstrates that the series of novel extrusion processes can be further optimized to create magnesium alloys with excellent strength-ductility.

Achieving high strength-ductility synergy in Mg-Gd-Zn-Zr alloy by controlling extrusion processes parameters

The high rare earth content in current magnesium alloys poses environmental and economic challenges. To address this issue, this study designs a Mg-7.5Gd-6Zn-0.5Zr alloy (GZ76, wt.%) with low rare earth content, high strength, and excellent ductility. The morphology of the as-cast GZ76 alloy is characterized by a dendritic structure consisting of an α-Mg matrix and interdendritic zones comprising W + I phases, interspersed with fragmentary Zn-Zr phases. Furthermore, the extrusion process is employed to meticulously control the microstructure and enhance the mechanical properties of the alloy. This research focuses on investigating the effects of extrusion parameters on magnesium alloys to optimize their extrusion processing conditions. Through systematic manipulation of the extrusion ratio and extrusion speed, a comprehensive analysis is conducted to examine their impacts on grain refinement, texture evolution, distribution of second phase, and mechanical properties of extruded magnesium alloys. The results indicate that due to the insufficient recrystallization process, the microstructure of the as-extruded GZ76 alloys exhibits a bimodal structure, encompassing both fine recrystallized grains and coarse unrecrystallized grains. At larger extrusion ratio, a faster extrusion speed leads to superior mechanical properties of the alloy. Conversely, at smaller extrusion ratio, a slower extrusion speed is more favorable for achieving higher strength. These findings provide valuable insights into optimizing the extrusion parameters for enhancing the performance of magnesium alloys in engineering applications.

High-strength and high-plasticity ZK60 magnesium alloy prepared by rapid solidification and high-speed extrusion

The extrusion speed of ZK60 magnesium alloy is usually lower than 5 m/min. The rapidly solidified (RS) ZK60 magnesium alloy extruded at 350 ℃ with die-exit speeds of 10 m/min, 20 m/min and 30 m/min was investigated. The results reveal that after the RS ZK60 alloy was extruded at different die-exit speeds, the average size of dynamically recrystallized grains is 1.19–1.40 μm, the percent of high-angle grain boundaries (HAGBs) become larger with the average orientation degree of 57.83 ° to 54.81 °, the intensity of texture at (0001)<1̅100> is below 3.4, and the Schmid factors of the prismatic and pyramidal planes reach the high value of no lower than 0.42 overall, while no coarse MgZn phase was observed. The yield tensile strength, ultimate tensile strength and elongation of the RS as-extruded ZK60 magnesium alloy change slowly from 321 to 299 MPa, -355–348 MPa, and -23–27 % when the die-exit speed increase from 10 to 30 m/min, respectively. The ultra-fine grains and disappearance of the coarse low melting-point MgZn phase are the main reasons for the high-speed extrusion, high strength, high plasticity and low texture of the RS as-extruded ZK60 magnesium alloy.

Effects of extrusion temperature on the microstructure and mechanical properties of low-alloyed Mg-Bi-Ca-Mn alloy

A new rare earth-free low-alloyed Mg-0.5Bi-0.8Ca-0.8Mn (wt.%) alloy was prepared at three extrusion temperatures (225, 250 and 275 °C). The effects of low-temperature extrusion on the microstructure and mechanical properties of the alloy were studied. Experimental results show that the dynamic recrystallization (DRX) grains are significantly refined by low-temperature extrusion, and the dynamic recrystallization process is further delayed by the Mn precipitate phase, resulting in a bimodal structure composed of ultrafine DRXed grains and coarse undynamic recrystallized (unDRXed) regions. At an extrusion temperature of 225 °C, the grain size was significantly refined, with an average DRXed grain size of 0.84 μm and a tensile yield strength of 418 MPa. Compared with other extruded magnesium alloys, the ultra-fine DRXed grains, strong basal fiber texture, high Schmid Factors of pyramidal <c + a> slip in the unDRXed regions, and along with a certain amount of second phase (Mg2Ca) distributed along the grain boundaries and nano-Mn particles uniformly distributed in the matrix, are the main reasons for the strength enhancement of low-temperature extruded magnesium alloys. The orientation of the DRXed grains in the alloy after extrusion at 250 °C is more random, which improves ductility. In addition, when the extrusion temperature reaches 275 °C, the alloy shows a fully recrystallized structure and exhibits rare earth (RE)-texture, obtaining high ductility but decreasing strength. This study provides a new idea for the development of high-strength Mg-Bi-based magnesium alloys by adjusting the extrusion temperature and alloying elements. This new high-strength and low-alloyed Mg-Bi-based alloy will help to enrich the series of high-performance, rare-earth free, low-cost extruded Mg alloy with certain application prospects.

High-speed deformation behaviour of 45° extruded magnesium alloy under quasi-in-situ conditions

In this study, quasi-in-situ electron backscatter diffraction was employed to investigate the microstructural evolution and deformation behaviour of ZK60 magnesium alloy with an initial 45° extruded state orientation under two high-speed impacts. The experimental results demonstrated that the deformation of the alloy mainly depended on slip and [Formula: see text] tension twinning. With the increase of deformation, the [Formula: see text] tension twins nucleated continuously, and there were stretching twin variants that were 60° away from the original stretching twins. In addition, compared with the conventional orientation (extrusion direction), 45° samples were easier to activate various slips under high-strain rate deformation conditions, especially ⟨c + a⟩ slips.

Grain refinement and strengthening mechanism of AZ31 magnesium alloy formed by pre-upsetting alternating forward extrusion

The pre-upsetting deformation process was added before the alternating forward extrusion forming, which can significantly refine the grains and improve the mechanical properties while reducing the load. The effects of 14%, 25%, 36% pre-upsetting deformation on the microstructure and mechanical properties of AZ31 magnesium alloy were investigated. The results show that the pre-upsetting alternating forward extrusion (UAFE) process can achieve significant grain refinement from 31.1 µm to 2.9–3.5 µm. With the increase of pre-upsetting deformation, the elongation at break tends to decrease and the tensile strength tends to increase. The comprehensive mechanical properties of U2AFE are the best, the yield strength and tensile strength are 203.1 MPa and 299.0 MPa respectively, and the elongation at break is 12.5%. The enhancement of the pre-upsetting deformation process not only makes the basal plane of grains in the billet randomly distributed and weakens the basal plane texture, but also stores a large amount of strain energy and dislocation inside the billet, which accelerates the subsequent continuous dynamic recrystallization (CDRX) process of alternating extrusion. This provides scientific guidance and technical support for the research of high-performance magnesium alloy extrusion forming technology.

Improving the tension-compression asymmetry of ZK61 magnesium alloy through texture optimization in combined extrusion

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

Effect of basal texture on small crack behavior of magnesium alloy in very high cycle fatigue regime

AbstractThe behavior of small cracks in magnesium alloy is key to understanding very high cycle fatigue (VHCF), which is influenced by microstructure and deformation mechanism. This study explores how basal texture affects VHCF failure mechanisms in extruded magnesium alloys. Findings reveal that faceted and rough morphologies characterize fracture surfaces during crack initiation and early propagation, respectively. Basal texturing inhibits basal slipping during faceted‐like crack initiation while compression twinning dominates deformation during early propagation, contributing to rough zones. Stress intensity factor and plastic zone size analysis indicates significant influence of basal texture on VHCF failure mechanisms but with limited effect on stable propagation.

Controlled radial deformation of AZ31B magnesium alloy bar during cyclic rotating-bending process

Extruded magnesium alloy bars are susceptible to uneven microstructure after the heat treatment process, which is characterised by coarse grain size in the surface, thus affecting the further processing properties of the overall bars. In this paper a new cyclic rotating-bending (CRB) process is proposed to improve the microstructure by achieving a gradient plastic deformation of the bars from the surface to the core. The paper is based on finite element simulations to qualitatively and quantitatively investigate the plastic strain distribution and evolution in the middle radial section of the bar under different CRB processes. In addition, the influence on the microstructure distribution under the processes is also further clarified. The results show that during CRB deformation, the plastic strain in the middle radial section of AZ31B magnesium alloy bars gradually decreases from the surface to the core radially, and the plastic strain in the surface is significantly positively correlated with the bending angle and the period of rotation. When the bending angle reaches 150°–170° and the period of rotation reaches 30 r, the section of the bars is fully plastic deformed. Simultaneously, compared to the initial microstructure, significant twinning deformation occurs in the surface of the bars after different CRB processes, which further promotes grain refinement.

Influence of Pre-Tension on Free-End Torsion Behavior and Mechanical Properties of an Extruded Magnesium Alloy.

In this study, the influence of pre-tension on free-end torsion behavior and compression mechanical properties and micro-hardness of an extruded AZ31 Mg alloy was investigated using electron backscatter diffraction (EBSD), compression testing and micro-hardness testing. The result indicates that pre-tension can cause significant dislocation strengthening, which can increase the torsion yield strength and make the shear stress-shear strain curve of the pre-tension sample almost parallel to that of the as-extruded sample during plastic deformation stage. Texture in edge position on the cross-section of both the pre-tension and as-extruded samples can be rotated towards the extrusion direction by about ~30° by free-end torsion. The Swift effect is mainly responsible for the occurrence of massive extension twins in the central region. In contrast, normal stress is the main cause of extension twins occurring in the edge region. However, the effect of extension twins on micro-hardness is less than that of dislocations. The micro-hardness of both free-end torsion specimens increases almost linearly with increasing distance from center to edge on the cross-section. Nevertheless, the increase in micro-hardness of the pre-tension and then torsion sample is inconspicuous because pre-tension leads to dislocation proliferation and dislocation accumulation saturation. The result also indicates that both pre-tension and free-end torsion can lead to dislocation strengthening, which can obviously increase the micro-hardness and compressive yield stress. The underlying mechanisms were explored and discussed in detail.

Investigation on the inhomogeneous deformation of magnesium alloy during bending using an advanced plasticity model

In the present work, an advanced plasticity model is established to character the anisotropic and asymmetric yielding and hardening behaviors of magnesium alloy. This model is comprised of the stress invariant-based Yoon2014 yield function, non-associated flow rule and yield surface-interpolation method in the description of distortional hardening. For effectively numerical implementation of the plasticity model, a semi-explicit stress integration scheme based on the return mapping method is provided. The implemented model is then applied to simulate the inhomogeneous deformations during three-point bending of an extruded magnesium alloy. Simulation results show that there are three distinct zones in the bent plate according to its deformation patterns, i.e., the compressive inner zone, the tensile outer zone, and the central zone which experiences tensile, then compressive and again tensile deformations. Compared to the counterpart Hill48 function, Yoon2014 function has better performance in simulating the inhomogeneous deformations of magnesium alloy.

Simulation of the Cyclic Stress–Strain Behavior of the Magnesium Alloy AZ31B-F under Multiaxial Loading

Under strain control tests and cyclic loading, extruded magnesium alloys exhibit a special mechanism of plastic deformation (“twinning” and “de-twining”). As a result, magnesium alloys exhibit an asymmetric material behavior that cannot be fully characterized with the typical numerical tools used for steels or aluminum alloys. In this sense, a new phenomenological model, called hypo-strain, has been developed to correctly predict the cyclic stress–strain evolution of magnesium alloys. On this basis, this work aims to accurately describe the local cyclic elastic–plastic behavior of AZ31B-F magnesium alloy under multiaxial cyclic loading with Abaqus incremental plasticity. The phenomenological hypo-strain model was implemented in the UMAT subroutine of Abaqus/Standard to be used as a design tool for mechanical design. To evaluate this phenomenological approach, the results were correlated with the uniaxial and multiaxial proportional and non-proportional experimental tests. In addition, the estimates were also correlated with the Armstrong–Frederick nonlinear kinematic hardening model. The results show a good correlation between the experiments and the phenomenological hypo strain approach. The model and its implementation were validated in the strain range studied.

Research Progress on Microstructure Evolution and Strengthening-Toughening Mechanism of Mg Alloys by Extrusion.

Magnesium and magnesium-based alloys are widely used in the transportation, aerospace and military industries because they are lightweight, have good specific strength, a high specific damping capacity, excellent electromagnetic shielding properties and controllable degradation. However, traditional as-cast magnesium alloys have many defects. Their mechanical and corrosion properties cause difficulties in meeting application requirements. Therefore, extrusion processes are often used to eliminate the structural defects of magnesium alloys, and to improve strength and toughness synergy as well as corrosion resistance. This paper comprehensively summarizes the characteristics of extrusion processes, elaborates on the evolution law of microstructure, discusses DRX nucleation, texture weakening and abnormal texture behavior, discusses the influence of extrusion parameters on alloy properties, and systematically analyzes the properties of extruded magnesium alloys. The strengthening mechanism is comprehensively summarized, the non-basal plane slip, texture weakening and randomization laws are comprehensively summarized, and the future research direction of high-performance extruded magnesium alloys is prospected.

A mesoscopic damage model for the low-cycle fatigue of an extruded magnesium alloy

This paper presents a novel mesoscopic damage model to characterize the low-cycle fatigue damage evolution of an extruded AZ31 magnesium (Mg) alloy, taking into account the effect of twinning. The damage caused by the slip bands (SBs)–twin boundaries (TBs) and SBs–grain boundaries (GBs) interactions is treated based on the Tanaka–Mura model and the Eshelby inclusion theory. Strain energy values at the TBs and GBs are defined as the TB and GB damage variables, respectively. Explicit formulae for the TB and GB damage evolution are derived from the characteristics of the {101¯2} extension twin and the basal texture. A fracture energy-based crack initiation criterion is established, and the proposed damage model is validated against the existing experimental results. The model demonstrates its ability to reproduce the damage evolution processes, and the predictions of the crack initiation life are within the twice error band.

Identifying the effect of coherent precipitates on the deformation mechanisms by in situ neutron diffraction in an extruded magnesium alloy under low-cycle fatigue conditions

As a new class of heat-treatable magnesium alloys, the low-alloyed Mg-Al-Ca-Mn alloy has great engineering potential because of its excellent extrudability and high strength by the dispersion of Guinier-Preston (G.P.) zones. The complex deformation mechanisms associated with hexagonal crystals, the interactions between defects with such G.P. zones, as well as their impacts on fatigue lifetime, are all critical issues before the actual deployment of such materials. In this study, this type of Mg alloy with and without G.P. zone dispersion during cyclic deformation was investigated by in situ neutron diffraction measurements. The relationship between the macroscopic cyclic deformation behavior and the microscopic response (particularly twinning and detwinning) at the grain level was established. The general deformation mechanism evolution in samples under the solution-treated (S.T.) state was generally similar to that in samples under the peak-aged (P.A.) state. Both samples plastically deformed by extension twinning during compression, and by a sequential process of detwinning and dislocation motion under reverse tension. Results suggest that the precipitates provided the greatest strengthening against the prismatic slip (∼ 45% increase), the moderate to the {101¯2} extension twinning (∼ 27 %), and the least to the basal slip (∼ 11% increase). The P.A. samples have shorter fatigue lifetime primarily due to the excessive dislocation pileups and the higher backstress that promote crack initiation.

Evolution of microstructure and texture of AZ80 magnesium alloy under hot torsion with constant decreasing temperature rate

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.

Microstructure and properties of biomedical Mg-Zn-Ca alloy at different extrusion temperatures

Due to its good biocompatibility, magnesium alloy has been greatly developed in the application field of absorbable implant metal materials in recent years. At the same time, the disadvantages of magnesium alloy materials are more obvious. Because of the poor mechanical properties of as-cast magnesium alloy, the bearing capacity as an implant is insufficient. In this paper, the self-made cast magnesium alloy was strengthened by extrusion at three extrusion temperatures, and then the grain refinement and phase composition of the extruded magnesium alloy were investigated by optical microscope and X-ray diffractometer. The grain shape, recrystallization volume fraction, grain orientation and microstructure of magnesium alloy at different extrusion temperatures were studied by quasi-in-situ electron backscattering diffraction (EBSD). Through tensile test, the mechanical properties of magnesium alloy under different extrusion parameters were studied. It was found that the lower the extrusion temperature, the higher the tensile strength of the material. This paper aims to improve the mechanical properties of magnesium alloys, and provide theoretical and practical guidance for the preparation, processing and application of high-performance medical magnesium alloys.

Dynamic Recrystallization Mechanism and Texture Evolution during Interactive Alternating Extruded Magnesium Alloy

Dynamic Recrystallization Mechanism and Texture Evolution during Interactive Alternating Extruded Magnesium Alloy

Evolution of primary and secondary twins during tensile cyclic loading in magnesium alloy ZM21 by quasi in situ EBSD

Large-scale microscopy at consecutive strains using quasi in situ EBSD was used to monitor the texture evolution in specific areas of extruded magnesium alloy ZM21 samples under cyclic tensile loading-unloading. Twin formation throughout the various cycles is highly dependent on slip and twin activity in the neighboring grains, so slip-trace analysis was conducted to monitor the activity of various slip systems. Slip traces were observed on three different glide planes: prismatic plane, first-order pyramidal plane, and second-order pyramidal plane. Formation of primary (including extension and contraction) twins and secondary twins was investigated in detail by overlapping the EBSD maps after pre-compression and after subsequent tension. Parent grains and twins were classified based on their orientations with respect to the ED (loading direction). The inverse pole figure map for the twins was plotted for the ED to calculate the position of the c-axis for twins. All extension twins that formed under reverse loading were located within 45°–90° of the ED axis, whereas the twins that formed during pre-compression were located within 45° of the ED axis. Extension twins are formed during tension loading perpendicular to the pre-existing twins from pre-compression (which have undergone a detwinning process under load reversal). Twin residues from compression interact with grain boundaries or new twins that have formed within the grains during tensile loading. Such interactions between twins and dislocations can result in damage-accumulation mechanisms which lead to crack initiation.

Correlation between stress state and crystal orientation distribution in alternating back extrusion of magnesium alloy

Deformation prediction and load evaluation were the keys to study the flow characteristics and microstructure evolution of magnesium alloy during alternating back extrusion (ABE). Firstly, the slip line field distribution at different downward loading depths of the split stem was determined by finite element simulation in this paper. After reasonably dividing into multiple rigid blocks, the extrusion load theoretical model was constructed based on the upper bound approach. On this basis, the stress state of the deformed billet was explored, which was related to the crystal preferred orientation of AZ31 magnesium alloy after ABE. The research results showed that the extrusion load model was consistent with the time-load curve trend of finite element simulation, and the predicted load in the initial stage of extrusion was about 8.14% higher than the finite element result. With the increase of downward loading depth of the split stem, the mean grain size of ABE in one loading cycle decreased to 6 μm, and the grain refinement reached 90%, which promoted the deep refinement of grain size. Affected by the maximum principal stress, the crystal orientation was segregated along with the stress distribution. The cooperative regulation law of deformation behavior and microstructure evolution for magnesium alloy during ABE was clarified, and the construction of the load theoretical model provided scientific guidance for the selection of deformation equipment and the formulation of research programs.