Microstructure Of Magnesium Alloy Research Articles

Mechanical properties and microstructure of magnesium alloy with in situ formed Al2RE phases

The advancement of magnesium alloys has historically faced challenges due to their inherently low modulus and the inverse relationship between modulus and ductility. In this study, an Mg-15Gd-8Y–11Al-0.3Mn alloy containing Al2RE phases was developed through an in-situ synthesis process, exhibiting exceptional mechanical properties, including a high elastic modulus of 57.6 GPa coupled with a satisfactory elongation of 7.3 %. The findings indicate the presence of polygonal Al2RE phases of varying sizes within the alloy, with α-Mg observed in some Al2RE phases, forming a coherent interface. The grain size of the alloy was refined, and the dimensions of the Al2RE particles were reduced through the extrusion process. The effective strain transfer between α-Mg and Al2RE, facilitated by the coherent interface, endowed the alloy with commendable ductility, even at a substantial Al2RE volume fraction of 23 %. Furthermore, the formation of the Al2RE phase was identified as the key contributor to the alloy's enhanced modulus. This study provides novel insights for the engineering of high-modulus magnesium alloys, thereby paving the way into their broader industrial application.

Enhancing yield strength and quantifying relationship with microstructure in magnesium alloys through work hardening

This paper explored how the work hardening process enhances the yield strength (YS) of magnesium alloy and established a novel quantitative relationship between microstructure and YS. The YS of an extruded MgNdZnZr alloy was nearly tripled by rotary swaging at 200 °C, attributing to dislocation accumulation, grain fragmentation, and basal texture formation. A modified Hall–Petch relationship (GM–HP) was established by introducing the equivalent orientation factor and dislocation density to accurately quantify the YS and the contribution of each strengthening mechanism. The contributions of dislocation hardening and grain boundary strengthening were multiplied by the strong basal texture. This paper offered valuable insights and guidance for designing and optimizing high-strength wrought magnesium alloys and their plastic processing methods.

Phase Field Simulation of the Effect of Second Phase Particles with Different Orientations on the Microstructure of Magnesium Alloys.

In this study, the phase field method has been used to study the effect of second phase particles with different shapes and different orientations on the grain growth of AZ31 magnesium alloy, after annealing at 350 °C for 100 min. The results show that the shape of the second phase particles would have an effect on the grain growth; the refinement effect of elliptical particles and rod-shaped particles was similar, and better than the spherical particles; the spatial arrangement direction of the second phase particles had no significant effect on the grain growth. On the other hand, when the microstructure of AZ31 magnesium alloy contained second phase particles with different shapes, the effect of mixing different shapes of second phase particles on the grain refinement was enhanced gradually with the decrease im the volume fraction of spherical particles.

Atomic simulation study on the effect of nanotwin on the compression behavior of Mg–Y alloys

Twining play an important role in adjusting the mechanical properties and microstructure in magnesium alloys. In this paper, molecular dynamics simulation was used to study the deformation behavior of nanotwin boundaries, simulating the compression deformation of polycrystalline Mg–Y magnesium alloys containing nanotwin boundaries and a double crystal with {10¯12} nanotwin boundary, respectively. It was found that the nanotwin boundaries can inhibit the movement and expansion of dislocations during compression deformation, and this inhibition would be enhanced with the increase of the width of nanotwin. The twinning and basal <a> slip can coordinate the deformation of magnesium alloy, and nanotwin can inhibit the activation of pyramidal <c+a> slip. The nanotwin boundaries could reduce the stress concentration and improve the local strain unevenness. The more uniform the distribution of nanotwin boundaries was, the smaller the degree of stress concentration would be. When a force was perpendicular to the nanotwin boundary, nanotwin tended to nucleate, growth and expansion, and consume a large number of dislocations, so the failure time of the sample was delayed.

Effect of Sm on twinning behavior of Mg-Gd-Y-Zr alloy at room temperature compression

Twining plays an important role in adjusting the mechanical properties and microstructure in magnesium alloys at room temperature deformation. In this work, the Mg-6Gd-3Y(-3Sm)-0.5Zr alloy was compressed at room temperature to study the effect of the Sm element on the twinning behavior. The results showed that twin of Mg-6Gd-3Y(-3Sm)-0.5Zr alloy after compressive deformation was {10–12} twin. In Mg-6Gd-3Y-0.5Zr alloy, there was coarse parallel twin, while in the Mg-6Gd-3Y-3Sm-0.5Zr alloy, there was a lot of fine cross twin. The variation of activated twin in Mg-6Gd-3Y-3Sm-0.5Zr alloy does not obey Schmid law. The activated cross twin variation in Mg-Gd-Y-Sm-Zr alloy can be divided into single-variant cross twin and multi-variant cross twin, both of which lead to changes in orientation differences. The large number of fine cross twin lead to matrix divided. This strengthened fine grains and the Mg-Gd-Y-Sm-Zr alloy showed high deformation stresses.

OPTIMIZATION OF WEAR STUDIES ON LASER CLADDED AZ61 MAGNESIUM ALLOY WITH NANO-TITANIUM DIOXIDE USING GREY RELATIONAL ANALYSIS

Laser cladding (LC) is mostly employed to enhance the wear resistance of magnesium alloy substrates. Adding nanoparticles will further strengthen the tribo surface properties, making them suitable for applications requiring lightweight components. This work investigated a dry sliding wear analysis for the laser-cladded AZ61 magnesium alloy with TiO2 nanoparticles at different volume ratios through the LC method. The spatial dispersion of the TiO2 nanoparticles in the AZ61 magnesium alloy microstructure was analyzed using scanning electron microscopy (SEM). The reinforcement ratio, sliding speed, and normal load were selected to study the tribo performance of the cladded surface. Coefficient of friction (COF) and wear loss analyses were performed using a pin on the disc dry sliding wear test. The effect of dry sliding variables on reinforcement ratio was analyzed with an orthogonal array experimental design. Grey relational analysis (GRA) studied multiple wear test responses to reveal optimal conditions to decrease the wear and friction coefficient of the AZ61 laser cladded surface. The reinforcement percentage of nanoceramic TiO2 particles in the AZ61 alloy surface was the most significant factor, contributing 97.76%, followed by a contribution of 0.26% by sliding speed and a normal load of 1.82%, confirmed with the grey relational grade. Both SEM and GRA confirmed that the reinforcement ratio of 10% exhibited lower wear loss and friction coefficient. The revealed wear mechanism operating on the worn surface of laser-cladded AZ61 magnesium alloy was micro-grooving exerted by a counter surface at all sliding conditions. This study shows that the LC of magnesium alloys will be preferred in sliding seal and lightweight gear applications.

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.

Quasi-in-situ EBSD study of fast static recrystallization evolution of AZ61 alloy at twinning interactions during electric pulse treatment

In this work, the quasi-in-situ electron backscattered diffraction (EBSD) is employed to investigate the static recrystallization occurring at the interface of deformation twinning interactions in liquid nitrogen temperature (LNT) rolled AZ61 alloy during electric pulse treatment (EPT). It was found that recrystallization nucleation occurred at the 10 1 ¯ 2 tensile twin (TTW) interaction, after which new grains and part of the original grains consumed 10 1 ¯ 2 TTW and grow up. By contrast, recrystallization nucleation occurs not only at the 10 1 ¯ 1 − 10 1 ¯ 2 double twin (DTW) interactions but also within twin boundaries during subsequent EPT. When multiple twins come into being in the exact grain, the recrystallization growth showed obvious directionality: first, recrystallization grains grow along with 10 1 ¯ 1 − 10 1 ¯ 2 DTW and 10 1 ¯ 1 CTW boundaries and consume them; then the 10 1 ¯ 2 TTWs are consumed and the growth direction of recrystallization grains shifts to along with their boundaries. • Static recrystallization induced by deformations twinning interactions in cryogenic rolled AZ61 alloy during electric pulse treatment has been investigated by using quasi- in-situ electron backscattered diffraction characterizations. • The effects of existing deformation twinning interactions on electrical pulse accelerated recrystallization behaviors have been analyzed. • By using cryogenic rolling and electrical pulse accelerated recrystallization, we suggest an effective way to tailor the microstructure of magnesium alloys.

An insight into a novel Mg2InSm prismatic plate in Mg-In-Sm alloy

• A novel Mg 2 InSm prismatic platelet can form in the aged Mg−In−Sm alloys. • The platelet has an aspect ratio of ∼25 and can keep a coherent relation with matrix. • The platelet is deemed as generalized β ″ with a (Mg 2 In)Sm-type D0 19 structure. Prismatic precipitate platelet is always purposefully designed in the microstructure of magnesium alloys due to its greater contribution to yield stress. In this study, with an introduction of In into Mg-Sm system, a category of novel { 10 1 ¯ 0 } α prismatic platelets has replaced thoroughly the traditional β ′ precipitate formed in magnesium rare earth (Mg-RE) alloys. Herein, the microstructural characteristics of platelet are investigated particularly by atomic scale scanning transmission electron microscopy. It is confirmed that the platelet has a Mg 2 InSm composition and can maintain a coherent relationship with α-Mg matrix. Importantly, on account of the similarities between In and Mg atoms, the Mg 2 InSm prismatic platelet could be structurally categorized as a generalized β ″ precipitate with a (Mg 2 In)Sm-type D0 19 structure when both In and Mg are regarded as an equivalent atom. Thus, the addition of In into Mg-Sm alloy induces the formation of β ″ precipitate. Furthermore, the formed β ″ prismatic platelets generally have a large average aspect ratio. The findings are of great significance to construct the effective precipitation strengthening phases and optimize the microstructure of Mg-based alloys. With an addition of In into Mg-Sm system, a type of novel { 10 1 ¯ 0 } α prismatic platelet has occurred and replaced the traditional β \prime precipitate. The prismatic platelet has a composition of Mg 2 InSm and can be categorized into a generalized β ″ phase with a (Mg 2 In)Sm-type D0 19 structure when Mg and In are deemed as a mixed atom.

Quasi-In-Situ Analysis of As-Rolled Microstructure of Magnesium Alloys during Annealing and Subsequent Plastic Deformation.

In this paper, quasi-in situ experiments were carried out on rolled AZ31 magnesium alloy sheets to track the recrystallization behavior of the rolled microstructure during the heat treatment process and the plastic deformation behavior during the stretching process. The as-rolled microstructures are classified into five characteristics and their plastic deformation behaviors are described. The research shows that annealing recrystallization leads to grain reorganization, resulting in the diversity of grain orientation, and it is easier to activate basal slip. Recrystallization preferentially nucleates in the regions with high stress, while it is difficult for recrystallization to occur in regions with low stress, which leads to the uneven distribution of the as-rolled structure of magnesium alloys. Slip can be better transmitted between small grains, while deformation between large and small grains is difficult to transmit, which can easily lead to the generation of ledges. Incomplete recrystallization is more likely to accumulate dislocations than complete recrystallization, and ledges are formed in the early stage of deformation. Microcracks are more likely to occur between strain-incompatible grains. It is of great significance to promote the application of rolled AZ31 magnesium alloys for the development of heat treatment and subsequent plastic working of rolled magnesium alloys.

Advances in degradation behavior of biomedical magnesium alloys: A review

Magnesium alloys have become promising biomedical metal materials because of their biocompatibility, degradability, and good mechanical properties. However, the rapid degradation of magnesium alloys and its associated effects have limited the applications of magnesium alloys. Alloying and preparation processes can reduce the degradation rate by changing the microstructure of magnesium alloys, such as grain size, porosity, formation of intermetallic compounds/second phases, etc. In this paper, the in vitro and in vivo degradation of magnesium alloys were reviewed in terms of degradation mechanism, influencing factors, and corrosion products. Composition design and manufacturing process were mainly discussed for controlling the degradation, and surface treatment and structural design were briefly described as control methods of degradation. This helps achieve the goal of controlled and predictable degradation rate of magnesium alloys.

Enhancing grain refinement and corrosion behavior in AZ31B magnesium alloy via stationary shoulder friction stir processing

Stationary shoulder friction stir processing (SSFSP) in thick AZ31B magnesium alloy was performed to refine the microstructure followed by evaluating corrosion behavior. The use of stationary shoulder exhibited low heat input and small temperature gradient across the thickness of stir zone (SZ). Moreover, smooth surface morphology with little flash was obtained. The probe-dominated SZ developed fine equiaxed uniform grain structure across the thickness of SZ, which in turn increased the corrosion resistance of SSFSPed alloy as compared to BM. SSFSPed alloy surface confirm uniform corrosion behavior with mud cracking and intergranual corrosion patterns instead of pitting corrosion in BM. This improvement in corrosion was attributed to homogenization of magnesium alloy microstructure by using low-heat-input stationary shoulder tool.

A novel 3D anisotropic Voronoi microstructure generator with an advanced spatial discretization scheme

At the microstructural scale, Voronoi tessellations are commonly used to represent a polycrystalline morphology. However, due to spherical growth of nuclei, an anisotropic tessellation with spatially varying elongated grain directions, which is present in many applications, cannot be obtained. In this work, a novel 3D anisotropic Voronoi algorithm is presented, together with its implementation and two application cases. The proposed algorithm takes into account preferred grain growth directions, aspect ratios and sizes in the definition of an ellipsoidal growth velocity field defined per grain. For applications in which a predetermined mesh is used, e.g. voxel-mesh based simulations, the grains are extracted in a straight-forward manner. In cases where a fully grain conforming discretization is desired, e.g. finite element simulations, a hexahedral mesh generator is incorporated to arrive at a discretization which can be directly used in microstructural modeling simulations. Two application cases are studied (a wire + arc additively manufactured and a magnesium alloy microstructure) in which the algorithm’s capability for curved, non-convex, periodic domains is shown. Furthermore, the resulting grain morphology is compared to experimental data in terms of grain size, grain aspect ratio and grain columnar direction distribution. In both cases, the algorithm adequately produces a representative volume element with convincing representativeness of the experimental data. The 3D anisotropic Voronoi algorithm is highly versatile in a wide range of application cases, specifically suitable for the generation of polycrystalline microstructures that include grains with spatially varying elongated directions.

AZ31 magnesium alloy tube manufactured by composite forming technology including extruded-shear and bending based on finite element numerical simulation and experiments

This paper presents a new forming technology for manufacturing the AZ31 magnesium alloy thin-wall tube. The direct extrusion process and continuous shearing-bending process are combined to produce thin-wall magnesium tube, abbreviated as “TESB” (tube extrusion-shearing-bending). The process has been studied based on the combination of experiments and numerical simulations, and the influences of temperatures, extrusion stresses, and friction factors on the forming process have been studied by Deform-3D simulation. And the mechanical properties and the grain size of the formed product have been tested. TESB technology has been proved to refine the grains of magnesium alloy tube effectively, and the mechanical property of the product can be improved. The better experimental extrusion conditions were also obtained by simulation, and the properties of the products under the condition of lubrication were better when the temperature was 400°C. Three-dimensional finite element modeling is used to investigate the plastic deformation behaviors of wrought magnesium alloy during TESB process. Numerical results indicate TES could increase the cumulative strains effectively by direct extrusion and additional shearings. Experiments show that microstructures of magnesium alloy fabricated by TESB process can be refined to 50% of the original grain size with more uniform distribution. TES process could improve hardness of magnesium alloy obviously by comparing with which fabricated by direct extrusion.

Constrained Voronoi models for interpreting surface microstructural measurements

Measurement and analysis of microstructures is an essential aspect of materials design and structural performance. In the case of surface experimental measurements such as digital image correlation (DIC), it is beneficial to know the subsurface microstructure to interpret the surface observations accurately. However, subsurface microstructures are expensive to obtain through three-dimensional (3D) tomography. Hence, it is of interest to generate these structures computationally. In this work, a generalized inverse Voronoi problem is used to grow an approximate representation of the 3D microstructure from a surface electron backscatter diffraction (EBSD) image. The novelty of the approach is that the surface microstructure is retained during the simulation. This technique is employed for the reconstruction of a recrystallized magnesium alloy microstructure. Crystal plasticity finite element modeling (CPFEM) was employed for comparing the predicted surface strains in the reconstructed 3D microstructures against experimentally measured data. It is observed that the surface strains of different 3D reconstructions are qualitatively similar to the experiment. However, strong basal slip activation in some subsurface grains can influence the choice of activated slip systems on surface microstructures. The results show the implications of performing a full 3D crystal plasticity analysis of measured surface data as compared to only analyzing a two-dimensional extruded microstructure.

Role of heat balance on the microstructure evolution of cold spray coated AZ31B with AA7075

A promising solid-state coating mechanism based on the cold spray technique provides highly advantageous conditions on thermal-sensitive magnesium alloys. To study the effect of heat balance in cold spray coating on microstructure, experiments were designed to successfully coat AA7075 on AZ31B with two different heat balance conditions to yield a coated sample with tensile residual stress and a sample with compressive residual stress in both coating and substrate. The effects of coating temperature on the microstructure of magnesium alloy and the interfaces of coated samples were then analyzed by SEM, EBSD, TEM in high- and low-heat input coating conditions. The interface of the AA7075 coating and magnesium alloy substrate under both conditions consists of a narrow-band layer with very fine grains, followed by columnar grains of magnesium that have grown perpendicular to the interface. At higher temperatures, this layer became wider. No intermetallic phase was detected at the interface under either condition. It is shown that the microstructure of the substrate was affected by coating temperature, leading to stress relief, dynamic recrystallization and even dynamic grain growth of magnesium under high temperature. Reducing the heat input and increasing the heat transfer decreased microstructural changes in the substrate.

Influence of extrusion conditions on microstructure and mechanical properties of Mg-2Gd-0.3Zr magnesium alloy

In general, different extrusion conditions will affect the microstructure of magnesium alloys and further determine the mechanical properties. The effects of extrusion parameters and heat treatment processes such as extrusion speed, pre-forging, annealing time, extrusion ratio and cooling rate on the microstructure, texture evolution and tensile properties of Mg-2Gd-0.3Zr alloys were investigated in this study. Compared with the as-cast alloy, the extrusion process significantly refines the grains and exhibit the rare earth texture. With the increase of extrusion speed and annealing time, the growth of recrystallized grains is accelerated, leading to the increase of elongation. Large pre-forging deformation achieves to refine the grains by promoting recrystallization nucleation, resulting in increased strength of Mg-2Gd-0.3Zr alloy. Decreasing the extrusion ratio or increasing the cooling rate will introduce coarse un-DRXed grains, which transformed the texture into the basal texture. In particular, the effect of rapid cooling on refining the recrystallized grains is also obvious. Different extrusion conditions influence the mechanical properties of the Mg-2Gd-0.3Zr alloy through the grain size, proportion of non-recrystallization region and texture type.

Microstructure Evolution and Mechanical Properties of AZ31 Magnesium Alloy Sheets Prepared by Low-Speed Extrusion with Different Temperature

AZ31 magnesium alloy sheets were prepared by low-speed extrusion at different temperatures, i.e., 350 °C, 400 °C, and 450 °C. The microstructure evolution and mechanical properties of extruded AZ31 magnesium alloy sheets were studied. Results indicate that the low-speed extrusion obviously improved the microstructure of magnesium alloys. As the extrusion temperature decreased, the grain size for the produced AZ31 magnesium alloy sheets decreased, and the (0001) basal texture intensity of the extruded sheets increased. The yield strength and tensile strength of the extruded sheets greatly increased as the extrusion temperature decreased. The AZ31 magnesium alloy sheet prepared by low-speed extrusion at 350 °C exhibited the finest grain size and the best mechanical properties. The average grain size, yield strength, tensile strength, and elongation of the extruded sheet prepared by low-speed extrusion at 350 °C were ~2.7 μm, ~226 MPa, ~353 MPa, and ~16.7%, respectively. These properties indicate the excellent mechanical properties of the extruded sheets prepared by low-speed extrusion. The grain refinement effect and mechanical properties of the extruded sheets produced in this work were obviously superior to those of magnesium alloys prepared using traditional extrusion or rolling methods reported in other related studies.

Relationship between Deep Drawability and Microstructure of Magnesium Alloy

Relationship between Deep Drawability and Microstructure of Magnesium Alloy

Effect of compression deformation on the distortion energy and semi-solid microstructure of Mg-6Al-0.9Gd alloys

In order to investigate the effect of distortion energy on the microstructure of magnesium alloys prepared by strain induced melt activation (SIMA) process and partial remelting, Mg-6Al-0.9Gd magnesium alloys were deformed at 200 °C with 0-20% compression ratios, and the relationship between deformation and eutectic melting activation energy was established based on differential scanning calorimetry (DSC) analysis, thereby determining the distortion energy at different compression ratios. The results showed that distortion energy increased with increasing compression ratio, which contributed to the morphological transition from dentrictic to equiaxed structure, and accelerated the formation of liquid phase during subsequent partial remelting. All things (grain size, liquid fraction and distribution in the semi-solid microstructure) considered, the optimal compression ratio for this paper was 20%.