Rare Earth Magnesium Research Articles

Microstructural evolution and properties analysis of laser surface melted and Al/SiC cladded magnesium-rare earth alloys

The influence of laser surface melting and Al–SiC cladding on the microstructure, mechanical, and electrochemical properties of Mg-Gd-Y-Zn-Zr alloys was studied. The presence of α-Mg, Mg5(Gd,Y,Zn) and Mg10(Y,Gd)Zn phases in the melted layer and Al4C3, SiC, Si, Mg2Si and Mg17Al12 phases in cladded layer were confirmed from XRD results. Microstructures and chemical composition results also indicated a refined microstructure and re-distribution of the second phase. The finite element model (FEM) temperature profiles confirmed the variation in cooling rates of melted and cladded zones which supported the achieved microstructures. The microhardness values across the melted and cladded layers were significantly increased as a result of grain refinement, re-distribution of the second phases of the melted layer and the presence of hard-ceramic phases in the cladded layers. Potentiodynamic polarization studies revealed a decrease in corrosion current density (icorr) value and enhanced corrosion resistance of the laser melted alloy. The Al/SiC cladded layer showed a nobler shift in corrosion potential (Ecorr) and a significant decrease in icorr value due to the thick ceramic layer which acts as a barrier to the corrosive attack.

Grain refinement and weak-textured structures based on the dynamic recrystallization of Mg–9.80Gd–3.78Y–1.12Sm–0.48Zr alloy

We utilized electron backscatter diffraction to investigate the microstructure evolutions of a newly developed magnesium-rare earth alloy (Mg–9.80Gd–3.78Y–1.12Sm–0.48Zr) during instantaneous hot indirect extrusion. An equiaxed fine-grained (average grain size of 3.4 ± 0.2 µm) microstructure with a weak texture was obtained. The grain refinement was mainly attributed to the discontinuous dynamic recrystallization (DDRX) and continuous DRX (CDRX) processes during the hot indirect extrusion process. The twin boundaries formed during the initial deformation stage effectively increased the number of high angle grain boundaries (HAGBs), which provided sites for new grain nuclei, and hence, resulted in an improved DDRX process. Along with DDRX, CDRX processes characterized by low angle grain boundary (LAGB) networks were also observed in the grain interior due to effective dynamic recovery (DRV) at a relatively high temperature of 773 K and high strain rates. Thereafter, LAGB networks were transformed into HAGB networks by the progressive rotation of subgrains during the CDRX process.

High strength-ductility of heterogeneous sandwich Mg–Y alloys produced by high pressure torsion

Due to unique precipitation behavior, magnesium-rare earth (Mg-RE) alloys exhibit excellent strength. However, owing to the blocking effect of solid solute atoms on the slipping of dislocations, the plasticity of Mg-RE alloys becomes poor. In this work, HPT followed by solution and aging treatment is used to produce laminate heterogeneous Mg–Y alloys by sandwiching a hard layer and two soft layers. Specially, the interface transition region shows a gradient distribution of Y concentration and precipitation. The sandwich Mg–Y alloy attains an enhanced strength-plasticity synergy.

Mechanical behavior and texture evolution of WE43 magnesium-rare earth alloy in Split-Hopkinson Pressure Bar and Taylor Impact Cylinder Testing

Mechanical behavior and texture evolution of Mg rare-earth alloy WE43 is investigated for strain-rates 10−3/s to upwards of 105/s for the two material conditions - as-cast (AC) and T6 age hardened, rolled plate (RT6). The high strain-rate behavior is tested using both Taylor cylinder impact tests (TC) and split Hopkinson pressure bar tests (SHB) and bulk textures are obtained using neutron diffraction. Unlike the quasi-static strained material, AC and RT6 SHB retained high hardening rates throughout the test, even up to 30% true strain. Moreover, the high strain-rate data revealed that the RT6 material has a much higher strength than the AC material, but similar hardening rates despite significantly different initial texture. The flow stress near yield increased up to 10% for RT6 and up to 30% for AC as the strain-rate increased six orders of magnitude from quasi-static rates 10−3/s to 103/s. Neither material exhibited significant plastic anisotropy over the broad range of strain rates, despite the fact that the RT6 material had a moderately strong initial texture. In the TC tests, the geometric cross-sectional changes and texture along the cylinder from the cylindrical sample foot to head are measured and from the neutron diffraction texture analysis, upper-bound estimates of twin volume fraction are obtained as well as dislocation density from analyzing diffraction peak broadening. Recorded geometrical changes along several loading directions show that the material has deformed homogeneously under impact. Analysis of deformed textures indicates that {101¯2} extension deformation twinning occurred in the RT6 condition over the range of strain rates, with an upper bound estimate of 40% twin volume fraction for approximately 0.10-0.25 true strain. The peak texture components after the impact have their c-axes closely aligned with the impact direction. These observations are presented and rationalized in the paper.

Evaluation of the VDA 238–100 Tight Radius Bend Test for Plane Strain Fracture Characterization of Automotive Sheet Metals

Accurate characterization of the fracture limit in plane strain tension of automotive sheet metals is critical for the design and crash performance of structural components. Plane strain bending using the VDA 238–100 V-bend test has potential for proportional fracture characterization by avoiding a tensile instability. The VDA 238–100 V-bend test was evaluated using DIC strain measurement to characterize the plane strain fracture limit under proportional plane stress loading and to evaluate the effect of the VDA pre-straining methodology for ductile alloys upon the material response. The load-based failure criterion of the V-bend test was evaluated with DIC to monitor the development of surface cracking. The influence of the non-linear strain path imposed by the pre-straining procedure for ductile materials was then evaluated for three automotive alloys: an advanced high strength dual phase steel, DP1180, a rare-earth magnesium, ZEK100, and an AA5182 aluminum. A fracture criterion based on the load threshold was reasonable for the three alloys considered. Pre-straining in uniaxial tension prior to plane strain bending affected each alloy differently. The DP1180 was not affected by the non-linear strain path whereas the cumulative equivalent strain for the AA5182 and ZEK100 increased by strains of 0.07 and 0.05 strain, respectively. The non-linear strain path within the VDA pre-straining methodology creates ambiguity in comparing the fracture limits of different materials. The plane strain fracture limit for proportional loading can be readily obtained in the V-bend test with DIC strain measurement.

Influence of Rare Earth Elements in Magnesium Alloy - A Mini Review

In recent days, the use of Magnesium and its alloys is preferred in defence, automotive and aerospace industries where large size and complex components are required in light weight. Besides, magnesium alloys are used in computers, electronic devices and biomedical applications. Alloying magnesium with rare earth elements (RE) is used to develop the light alloys for the stated applications at elevated temperature. Rare earth magnesium alloys are having unique properties over other metals, including a high specific strength, low thermal conductivity, good damping capacity and good castability. In this review article, the recent development of rare earth magnesium alloys will be reviewed from the view point of novel alloying designs. It has been revealed that in ternary alloy system Mg-ZN-RE alloy exhibited high strength and ductility. This leads the researchers to investigate Mg-ZN-RE alloy recently.

High Strain Rate Compressive Behavior of As-Cast and Heat Treated Magnesium-Rare Earth Alloy at Low Temperatures

The deformation behavior and mechanical properties of magnesium-rare earth alloy (WE43) were investigated for as-cast and heat-treated conditions at a broad range of strain rates and temperatures. The study was focused on developing a constitutive relation for the alloy with respect to temperature and strain rate for the as-cast and heat treated conditions. The experimental results show higher strength of the alloy at lower temperatures. Heat treatment of the alloy has a remarkable effect on the alloy microstructure, where eutectic mixture dissolves and only rare earth rich precipitates are observed in the heat treated microstructure. This change in the microstructure was reflected in the measured tensile properties and heat treated alloy has higher strength due to strengthening effect of the fine precipitates. A constitutive model was established to describe the thermo-viscoplastic flow behavior of the hexagonal close-packed alloy in a broad range of coupled strain rates (0.0001/s–3055/s) and temperatures (77–296 K). The model predictions agree with the experimental results at both quasi-static and high strain rates. The results show the possibility of extending this work to develop time–temperature superposition procedures using the coupling parameters identified by the model.

Uniaxial Ratcheting of Extruded Mg-10Gd-3Y Alloy under Stress-Controlled Cyclic Tension

Uniaxial ratcheting behavior of an extruded Mg-10Gd-3Y rare-earth magnesium alloy was studied by performing stress-controlled cyclic tension experiments in ambient air. The effects of mean stress and stress amplitude on the ratcheting response and the ratcheting lifetime were explored. As the mean stress or the stress amplitude was increased, the ratcheting strain multiplied, whereas the ratcheting lifetime was shortened. Compared to the conventional Mg alloys, the addition of rare-earth elements suppressed the twinning/de-twinning events and restricted the development of ratcheting strain. In addition, dynamic precipitations were developed during the ratcheting deformation of the Mg-10Gd-3Y alloy at room temperature. This cyclic stress-induced dynamic precipitation is thought to play a critical role in the strong cyclic hardening exhibited during the ratcheting deformation of the Mg-10Gd-3Y alloy. A modified fatigue parameter, which takes account for both the effects of mean stress and stress amplitude, was proposed to well predict the ratcheting lifetime of the Mg-10Gd-3Y alloy.

Deformation behavior and microstructure evolution of rare earth magnesium alloy during rotary extrusion

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.

Development Strategies for China’s Advanced Magnesium Alloy Industry Toward 2035

In this paper, we introduce the development status of China’s magnesium alloy material industry, analyze the main problems faced by its development in China and abroad, and prospect the future market demand in China for magnesium alloy materials such as high-performance rare earth–magnesium alloys with lightweight structures, magnesium alloys with high strength and high thermal conductivity, magnesium alloys with high strength and high electrical conductivity, and ultra-high-strength magnesium alloys. We also present a phased development plan for the industry toward 2030 and 2035 and propose relevant strategies for promoting the sustainable development of this industry in China. These strategies include promotion of independent innovation capabilities, optimization in resource allocation, strengthening of corporate cooperation, establishment of a complete research system for magnesium alloy materials, and improvement in platform construction. To satisfy the demand for the advanced magnesium alloy materials by national economy, national major projects, and social sustainable development, China should optimize its scientific research system, optimize the industrial development pattern, create high-quality and efficient industries, improve relevant policy systems, and build a sophisticated talent system.

Effect of Zn addition on the microstructure and mechanical properties of Mg-0.5Ca-0.5RE magnesium alloy

The microstructure and mechanical properties of Mg–Zn-0.5Ca-0.5RE magnesium alloy, with zinc contents of 0, 2, 4, and 6 wt%, were studied. A significant effect of Ca and rare earth (RE) elements (via mischmetal addition) on the grain refinement of cast ingots was observed with the consequent enhancement of ultimate tensile strength (UTS). Moreover, while the grain size was refined by the addition of Zn, no significant α-Mg grain refinement occurred beyond 2 wt% Zn addition. The Mg12RE intermetallic compound was observed in all alloys while the Mg7Zn3 phase formed at the grain boundaries of Zn-containing alloys. Based on the competition of grain refinement as a favorable factor and formation of unfavorable grain boundary phases, the Mg–4Zn-0.5RE-0.5Ca (ZEX400) alloy showed the highest UTS among the cast alloys. Intense grain refinement introduced by the extrusion process and the fracturing and dispersion of the grain-boundary phases resulted in the significant enhancement of strength and ductility and the appearance of ductile fracture surface for the extruded Mg–4Zn-0.5RE-0.5Ca alloy. It was found that high Zn content (∼6 wt%) limits the usability and hot working temperature range of the alloys due to the problem of hot shortness and intergranular brittle fracture. Therefore, the addition of 4 wt% Zn was recommended for industrial practice. This work revealed the significant effects of alloying (with Ca, RE, and Zn) and hot extrusion process for microstructural refinement and enhancement of mechanical properties of Mg alloys.

Evolution Mechanism of Inclusions in H13 Steel with Rare Earth Magnesium Alloy Addition

Evolution Mechanism of Inclusions in H13 Steel with Rare Earth Magnesium Alloy Addition

A first-principles study of [formula omitted] phase in magnesium-rare earth binary systems

The formation energies, elastic constants, moduli and electronic structures of the coherent βF′ phase in eight different binary Mg-RE (RE = La, Ce, Pr, Nd, Pm, Sm, Eu and Gd) systems are calculated systematically by a first-principles method, and the interfacial energies between the βF′ phases and α-Mg matrix are also predicted. The results of these calculations indicate that for the alloys considered the βF′ phase has a higher moduli than the α-Mg phase. In terms of electronic structure, charge density plots show that the electrons concentrate among the RE atoms and their neighboring Mg atoms, and the density of states reveal the overlapping of the p-orbitals of Mg atoms and d-orbitals of RE atoms. These observations suggest that strong intermetallic bonds formed between RE atoms and neighboring Mg atoms inside the βF′ phases, which explains the shrinkage of the βF′ phases in 11¯00α and 〈0001〉α directions and the higher stiffness of the βF′ phases. The results also show that the rare earth systems in which βF′ has been observed (RE = Nd, Sm and Gd) have lower interface formation energies than the other Mg-RE systems. A comparison of the βF′ and β′ phases in the Mg-Gd system is also carried out to interpret experimental observations that, whilst these two phases can form simultaneously, the βF′ phase is less frequently observed.

Influence of Friction Stir Processing Parameters on Mg ZE 41-SiC Surface Composite

In this study, the influence of friction stir processing process parameters (FSP), such as tool rotational speed, tool traverse speed, and the tool tilt angle on the mechanical properties of Sic reinforced surface magnesium rare earth ZE41 alloy composite was studied. The process was carried at tool rotational speeds of 710, 900, 1120, 1600, 1400 and 1800 rpm, tool traverse speeds of 16, 25, 40 and 63 mm/min and tool tilt angle of degree 1. Nano-particles of SiC (40 microns) were used as reinforcements to produce a composite surface. The grain refinement of the processed specimens was analyzed using scanning electron microscope. It is observed from the results that FSP process parameters influenced the surface composite area, SiC particles distribution and micro hardness of the composite. The outcomes indicated that the higher micro hardness was obtained at rotational speed of 1100 RPM, traverse speed 40mm/min and tilt angle 10.

Microstructures and properties of as-cast rare Earth magnesium alloy with LPSO phase

The Mg-6Gd-2xY-xZn-0.6Zr (x = 0.5,1,1.5,2, wt%) alloys were prepared by conventional casting. With the increasing of Y and Zn content, the microstructure became finer and the size of the second phase gradually became larger. The results show that the forming of the LPSO phase significantly improves the mechanical properties of rare Earth magnesium alloy. And Mg-6Gd-3Y-1.5Zn-0.6Zr (wt%) alloy has the best mechanical properties and better damping capacity, while its tensile strength and elongation reached 216.64 MPa and 12.9%, respectively.

Electrodeposition of Pr-Mg-Co ternary alloy films from the choline chloride-Urea ionic liquids and their corrosion properties

This paper aims to obtain rare earth magnesium alloy with good adhesion and corrosion resistance. The work was concerned with the electrochemical behaviors of Co(II), Mg(II), Pr(III) on Pt and Cu electrodes in choline chloride-urea ionic liquids by electrochemical techniques of cyclic voltammetry. The electrodeposition conditions of Pr-Mg-Co ternary alloy films on copper substrate from the choline chloride-urea ionic liquids with different metal salts were investigated by potentiostatic electrolysis. The author has used scanning electron microscopy coupled with energy dispersive X-ray spectroscopy to study the surface morphology and composition of Pr-Mg-Co ternary alloy film, Polarization curves are tested. Results shows under −1.15 V voltage, the alloy films with evening is obtained when the concentration ratio of Pr(III)/Mg(II) is 4:3, and deposition time is 30 min .it showed that the content of Pr in the alloy film has reached up to 13.22 wt.%, and the morphology of black alloy coating is amorphous and has micro-cracks, which reflects the alloy films has good corrosion performance in alkaline solution. This can be attributed to its dense film structure and good adherence to the substrate. It provides some technology for the production of corrosion- resistant materials.

Direct observation of beta″ precipitate with a three-dimensional periodic structure in binary Mg–La alloy

It is a long-debated issue whether or not β′′ forms in magnesium-rare earth alloys. In this study, after solid solution and aging treatment, the binary Mg-3.0 wt% La alloys were characterized using atomic-resolution scanning transmission electron microscopy. A large number of β′′ metastable precipitate was captured successfully along [0001]α and 112¯0α directions. The [0001]α observation reveals that the inchoate β′′ is composed of single row of linked hexagonal rings. Under further aging, the expansion direction of the hexagonal ring is not limited to 112¯0α direction and the β′′ can reach a thickness of 5cβ′′ along [0001]α, demonstrating that the β′′ forms a three-dimensional periodic structure and the β′′ phase can form in binary MgLa alloy. Meanwhile, a planar defect with an ABCBA stacking fault can be formed usually in the interface between β′′ phase and α-Mg matrix, which contributes to alleviate the distortion of adjacent α-Mg matrix.

The Effect of ECAP Temperature on the Microstructure and Properties of a Rolled Rare Earth Magnesium Alloy.

Deformation of an as-rolled rare earth Mg-2Y-0.6Nd-0.6Zr alloy, at different temperatures, was carried out along the BC (90° anticlockwise rotation of the samples after each ECAP pass) route by equal channel angular pressing (ECAP). The effects of the deformation temperature and the predeformation on the microstructure of the magnesium alloy were determined by the microstructure examination. The slip systems and texture change of the Mg-2Y-0.6Nd-0.6Zr alloy were investigated by X-ray diffraction (XRD) and electron backscattered diffraction (EBSD), after equal channel angular deformation. The results showed that after seven passes of rolling, the grain size in the Mg-2Y-0.6Nd-0.6Zr alloy was refined to approximately 22 µm and the slip occurred mainly by a cylindrical slip and a pyramidal slip. After one pass of ECAP at 340 °C, the internal average grain size was significantly reduced to 11 µm, the cylindrical diffraction intensity clearly weakened, and the pyramidal diffraction intensity increased. EBSD pole figure analysis revealed that the base texture of the rolled Mg-2Y-0.6Nd-0.6Zr alloy weakened from 24.31 to 11.34 after ECAP. The mechanical properties indicated that the tensile strength and elongation of the rolled Mg-2Y-0.6Nd-0.6Zr alloy reached maximum values, when the deformation temperature was 340 °C.

Mechanical response, twinning, and texture evolution of WE43 magnesium-rare earth alloy as a function of strain rate: Experiments and multi-level crystal plasticity modeling

This work adapts a recently developed multi-level constitutive model for polycrystalline metals that deform by a combination of elasticity, crystallographic slip, and deformation twinning to interpret the deformation behavior of alloy WE43 as a function of strain rate. The model involves a two-level homogenization scheme. First, to relate the grain level to the level of a polycrystalline aggregate, a Taylor-type model is used. Second, to relate the aggregate level response at each finite element (FE) integration point to the macro-level, an implicit FE approach is employed. The model features a dislocation-based hardening law governing the activation stress at the slip and twin system level, taking into account the effects of temperature and strain rate through thermally-activated recovery, dislocation debris formation, and slip-twin interactions. The twinning model employs a composite grain approach for multiple twin variants and considers double twinning. The alloy is tested in simple compression and tension at a quasi-static deformation rate and in compression under high strain rates at room temperature. Microstructure evolution of the alloy is characterized using electron backscattered diffraction and neutron diffraction. Taking the measured initial texture as inputs, it is shown that the model successfully captures mechanical responses, twinning, and texture evolution using a single set of hardening parameters, which are associated with the thermally activated rate law for dislocation density across strain rates. The model internally adjusts relative amounts of active deformation modes based on evolution of slip and twin resistances during the imposed loadings to predict the deformation characteristics. We observe that WE43 exhibits much higher strain-hardening rates under high strain rate deformation than under quasi-static deformation. The observation is rationalized as primarily originating from the pronounced activation of twins and especially contraction and double twins during high strain rate deformation. These twins are effective in strain hardening of the alloy through the texture and barrier hardening effects.

Influence of design and postprocessing parameters on the degradation behavior and mechanical properties of additively manufactured magnesium scaffolds

Magnesium shows promising properties concerning its use in absorbable implant applications such as biodegradability, improved mechanical strength and plastic deformability. Following extensive research, the first fixation and compression screws composed of magnesium rare earth alloys were commercialised, notably in the field of orthopaedic surgery. Preclinical and clinical follow-up studies showed that the rapid degradation of unprotected metallic Magnesium surfaces and concomitant hydrogen gas bursts still raise concern regarding certain surgical indications and need to be further improved. In order to enlarge the scope of further applications, the development of future magnesium implants must aim at freedom of design and reduction of volume, hereby enabling higher functionalised implants, as e.g. plate systems or scaffold grafts for bone replacement therapy. In order to overcome the boundaries of conventional manufacturing methods such as turning or milling, the process of Laser Powder Bed Fusion (LPBF) for magnesium alloys was recently introduced. It enables the production of lattice structures, therefore allowing for reduction of implant material volume. Nevertheless, the concomitant increase of free surface of such magnesium scaffolds further stresses the aforementioned disadvantages of vast degradation and early loss of mechanical stability if not prevented by suitable postprocessing methods. Magnesium scaffold structures with different pore sizes were therefore manufactured by LPBF and consequently further modified either by thermal heat treatment or Plasma Electrolytic Oxidation (PEO). Implant performance was assessed by conducting degradation studies and mechanical testing. PEO modified scaffolds with small pore sizes exhibited improved long-term stability, while heat treated specimens showed impaired performance regarding degradation and mechanical stability. Statement of SignificanceMagnesium based scaffold structures offer wide possibilities for advanced functionalized bioabsorbable implants. By implementing lattice structures, big implant sizes and mechanically optimized implant geometries can be achieved enabling full bone replacement or large-scale plate systems, e.g. for orthopedic applications. As shape optimization and lattice structuring of such scaffolds consequently lead to enlarged surface, suitable design and postprocessing routines come into focus. The presented study addresses these new and relevant topics for the first time by evaluating geometry as well as heat and surface treatment options as input parameters for improved chemical and mechanical stability. The outcome of these variations is measured by degradation tests and mechanical analysis. Evaluating these methods, a significant contribution to the development of absorbable magnesium scaffolds is made. The findings can help to better understand the interdependence of high surface to volume ratio Magnesium implants and to deliver methods to incorporate such lattice structures into future large-scale implant applications manufactured from bioabsorbable Magnesium alloys.