RE Alloys Research Articles

A Quantitative Phase Analysis by Neutron Diffraction of Conventional and Advanced Aluminum Alloys Thermally Conditioned for Elevated-Temperature Applications.

As the issue of climate change becomes more prevalent, engineers have focused on developing lightweight Al alloys capable of increasing the power density of powertrains. The characterization of these alloys has been focused on mechanical properties and less on the fundamental response of microstructures to achieve these properties. Therefore, this study assesses the quality of the microstructure of two high-temperature Al alloys (A356 + 3.5RE and Al-8Ce-10Mg), comparing them to T6 A356. These alloys underwent thermal conditioning at 250 and 300 °C for 200 h. Time-of-flight neutron diffraction experiments were performed before and after conditioning. The phase evolution was quantified using Rietveld refinement. It was found that the Si phase grows significantly (13-24%) in T6 A356, A356 + 3.5RE, and T6 A356 + 3.5RE alloys, which is typically correlated with a reduction in mechanical properties. Subjecting the A356 3.5RE alloy to a T6 heat treatment stabilizes the orthorhombic Al4Ce3Si6 and monoclinic β-Al5FeSi phases, making them resistant to thermal conditioning. These two phases are known for enhancing mechanical properties. Additionally, the T6 treatment reduced the vol.% of the cubic Al20CeTi2 and hexagonal ᴨ-Al9FeSi3Mg5 phases by 13% and 23%, respectively. These phases have detrimental mechanical properties. The Al-8Ce-10Mg alloy cubic β-Al3Mg2 phase showed significant growth (82-101%) in response to conditioning, while the orthorhombic Al11Ce3 phase remained stable. The growth of the beta phase is known to decrease the mechanical properties of this alloy. These efforts give valuable insight into how these alloys will perform and evolve in demanding high-temperature environments.

A magnesium alloy with ultrahigh Gd content manufactured by laser directed energy deposition: Heat treatment and microstructure evolution

High RE content is able to improve the age-hardening response of Mg–RE alloys, thus enhancing mechanical properties. Here, we successfully produce a Mg–22Gd–2Zn–0.4Zr (wt%) alloy with ultrahigh Gd content using laser directed energy deposition (LDED) and investigate the microstructure evolution during heat treatment. Results show that for the studied alloy, the yield strength is 333 MPa after solution at 520 °C for 2 hours and aging at 200 °C for 64 hours, superior to most existing Mg–Gd alloys, due to the high number density of the strengthening β' phase resulting from high supersaturation. During solution treatment, increasing the temperature improves the solution efficiency by reducing the holding time, while preventing the overgrowth of grains. The peak hardness is around 139 Hv for both 175 °C and 200 °C aging, indicating that the peak hardness of Mg alloys with high Gd content is insensitive to aging temperature. This research can serve as guidance for the heat treatment and microstructure control of high-Gd-content magnesium alloys.

Processing of high-strength thermal-resistant Al-2.2% cerium-1.3% lanthanum alloy rods with high electric conductivity by High Pressure Torsion Extrusion

A novel severe plastic deformation (SPD) process of High Pressure Torsion Extrusion (HPTE) was applied to the rods of the Al-2.2 wt.% Ce-1.3 wt.% La (Al–3.5RE) alloy. The microstructure, microhardness, the mechanical strength, thermal stability, and electrical conductivity of the alloy after HPTE and subsequent annealing have been investigated. It was demonstrated that HPTE processing can simultaneously increase yield strength from 127 to 225 MPa and electrical conductivity from 54.7% IACS to 55.7% IACS in this alloy. Such a remarkable combination of properties was achieved thanks to significant refinement of microstructure constituents: grain size of Al matrix was reduced down to 0.9 µm and initially continuous network of Al11RE3 phase was broken to micrometer- and nanometer-sized particles. Furthermore, the yield strength of the HPTE-processed Al–3.5 RE alloy remains stable at 230 °C for 1 h due to micrometer- and nanometer-sized particles that pin the grain boundaries. Therefore, HPTE processing of Al–RE alloys has a high application potential in the electric power industry.Graphical abstract

Microstructure evolution and mechanical properties of high strength and high conductivity Cu[sbnd]Fe alloy wire prepared by cold drawing

CuFe alloy wire is widely used in the field of electronic information because of its high strength and high conductivity. In this study, Cu-5Fe-0.1Si-0.3 Mg-0.05RE (La, Ce) alloys were prepared by cold drawing and heat treatment. The microstructure evolution of the alloy during deformation was studied by optical microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM). Three kinds of second phases with different sizes and shapes were successfully constructed in the designed alloys, including fibrous iron phase, submicron spherical iron phase and nano spherical phase. The strength of the alloy is greatly improved by drawing deformation, with only slight reduction of the conductivity. Through joint addition of Mg, Si and rare earth elements, the designed CuFe alloy wire rod has excellent overall properties. It's electrical conductivity, tensile strength, yield strength and elongation reached 63.8% IACS, 831 MPa, 730 MPa and 6.1%, respectively. Detailed characterizations of the alloys reveal that: the addition of Mg reduces solid solubility limit of iron in matrix and spaces between iron phases; the FeSi phase formed by Si and Fe promotes the precipitation of iron phase; and the addition of rare earth inhibits segregation of second phase, recovery and recrystallization of the alloy, and the coarsening of Fe phase. The mechanical properties of the alloy are improved by fiber strengthening, Hall-Petch strengthening and precipitation strengthening, respectively. The contributions of precipitation strengthening, fiber strengthening and Hall-Petch strengthening to yield strength are 65 MPa, 59 MPa and 277 MPa, respectively. The microstructure of dislocation and fibrosis is the main factor of alloy strengthening.

Microstructure and Tensile Properties of HPDC Mg–RE Alloys with Varying Y Additions

AbstractHigh-pressure die-casting Mg–2.6RE–xY (EW) alloys with Y contents between 0 and 3% (in wt%) were investigated for their microstructure and tensile properties. In the Y-containing alloy, the intermetallic phases at the grain boundaries consisted of skeletal Mg12RE phase, bulk Mg24Y5 phase and irregular Mg3Y phase, while {011} twins were observed in the Mg12RE phase. The yield strength was improved by Y addition at both room temperature and high temperatures. Compared with Y-free alloy, the yield strength of 3% Y alloy increased from 143.1 to 174.8 MPa and improved by 22.2% at room temperature, while it was increased from 72.2 to 104.6 MPa and enhanced by 44.9% at 300 °C. The area fraction of intermetallic phase increased dramatically from 14.5 to 18.4% with 3% Y addition. Second phase strengthening was the major contributor to the yield strength increase at ambient temperature. The increment of the area fraction of the high-thermally stable Mg–RE intermetallic phases with Y addition contributed to the consequent improvement in yield strength at high temperatures. At ambient temperature, the mechanism for the fracture of EW alloys was a ductile and quasi-cleavage fracture blend.

Order–Disorder Phase Transitions in Fe81Ga19–RE Alloys (RE = Dy, Er, Tb, Yb) According to Neutron Diffraction Data

Order–Disorder Phase Transitions in Fe81Ga19–RE Alloys (RE = Dy, Er, Tb, Yb) According to Neutron Diffraction Data

Precipitation behavior and mechanical properties of Mg-Nd-Sm-Zn-Zr alloy

A novel Mg-Nd-Sm-Zn-Zr alloy with promising age-strengthening effects has been successfully developed to meet the urgent needs of lightweight in the aerospace industry. The precipitation behavior and elastic properties of the nano-precipitates in the alloy have been revealed using transmission electron microscopy and first-principles calculation. The Guinier-Preston (GP) zones, lamellar γ′ precipitates, and granular β′ precipitates formed in the α-Mg matrix after aging at 190 °C for 3 h (under-aging stage). Notably, the alloy reached the peak-aging stage and achieved an excellent ultimate tensile strength of 266 MPa after aging for 18 h. These precipitates further transformed into the lamellar β′ and β1 precipitates, and the enclosed nano-strengthening structure was constructed by γ′, β′ and β1 precipitates. The precipitation sequence of the aged alloy was determined as the supersaturated solid solution (SSSS) → GP zones → β′/γ′ → β1. First-principles calculations and 3D visualization approach demonstrated that the addition of mixed light RE elements can effectively improve the elastic modulus and reduce the elastic anisotropy of β′ nano-precipitates. The Young's modulus (E), shear modulus (G), and anisotropy index (AU) of β′-Mg7(Nd,Sm) precipitates were 48.38 MPa, 18.79 MPa and 2.29, respectively. This study provides a theoretical and experimental basis for further research and development of novel high-performance Mg-light RE alloys.

Microstructure evolution and mechanical properties of Mg–Mn–RE alloy processed by equal channel angular pressing

Equal Channel Angular Pressing (ECAP) has been used to successfully produce ultrafine-grained ME21 alloy with a good strength-ductility synergy. The microstructure of the as-cast ME21 alloy and its evolution during the ECAP processing were characterized using a combination of optical microscopy (OM) and scanning electron microscopy (SEM). Fracture surfaces after tensile test were also characterized using SEM. Chemical analysis and phase identification were done by energy dispersive spectroscopy (EDS) and X-ray diffraction analysis, respectively. The combination of these techniques enabled the interpretation of the mechanical behavior during the various processing stages of the alloys. The ECAP process was performed up to 16 passes, producing a uniform ultra-fine grain (1 µm) ME21 alloy resulting from full dynamic recrystallization. At room temperature, the yield strength after 16 ECAP passes (191.4 MPa) was 251% higher than that of the as-cast ME21 alloy, accompanied by a good elongation of 8.1%. The hardness increased to 60.7HV which is about 52% higher than that of the as-cast alloy. These improvement in mechanical properties is due to the ultra-fine grains with high angle grain boundaries (HAGBs) and the precipitate strengthening effects of the uniformly dispersed fine precipitates of Mg12Ce and Mn formed as a result of the intense shear during the ECAP process.

Effect of aging on corrosion and discharge performance of AZ63-1.5RE alloy as anode in magnesium-dissolved oxygen seawater batteries

This study aims to understand how aging treatment affects corrosion resistance and discharge performance of AZ63-1.5 rare earth mischmetals (AZ63-1.5RE) alloy in low-power dissolved oxygen seawater batteries. Solutionizing and aging treatment at 180 °C, 210 °C, and 240 °C for 16 h, 20 h, and 24 h is used to investigate the effects of heat treatment on corrosion and discharge performance. An XRD pattern of alloys after solutionizing and aging indicates a change in crystalline orientation and an increase in Mg phases proportion. A reduction in self-corrosion of alloys is achieved through solutionizing and aging. With solutionizing and aging of the alloys, their discharge potentials is shifted to more negative values by about 0.01–0.02 V. The anodic efficiency also is improved significantly from 53.89% for the as-cast alloy to 67.55% for the aged alloy at 210 °C for 20 h. Following 24 h of discharge, the aged alloy at 210 °C demonstrated the highest polarization resistance. The favorable corrosion performance can be attributed to grain refinement of the β-Mg17Al12 phase, the increased contribution of the Al-RE corrosion-resistant phase, the low contribution of the layered phase in the matrix, and the formation of dense discharge products on the surface.

Evaluation of Thermal Stability and Its Effect on the Corrosion Behaviour of Mg-RE Alloys Processed by High-Pressure Torsion

The evolutions of microstructure and texture and the corrosion behaviour of low light rare-earth containing Mg-1.4Nd and low heavy rare-earth containing Mg-0.6Gd and Mg-0.4Dy (wt.%) were evaluated and compared after processing by high-pressure torsion (HPT) and isochronal annealing at 250 and 450 °C for 1 h using electron backscatter diffraction (EBSD) and electrochemical tests in a 3.5% (wt.%) NaCl solution. The EBSD results show that dynamic recrystallisation (DRX) was restricted in the Mg-1.4Nd alloy which led to a heterogenous deformation microstructure whereas the Mg-0.6Gd and Mg-0.4Dy alloys exhibited a homogenous deformation microstructure formed mostly of equiaxed dynamically recrystallised DRX grains. The HPT processing caused the development of a deviated basal texture in the three alloys. A good thermal stability of the three alloys was noticed after annealing at 250 °C. By contrast, annealing at 450 °C led to a homogenous equiaxed microstructure and weakening of texture for the Mg-1.4Nd alloy and a heterogenous bimodal microstructure with a stable basal texture for the Mg-0.6Gd and Mg-0.4Dy alloys. The HPT-processed Mg–RE alloys exhibited an improved corrosion resistance due to grain refinement. Thereafter, the corrosion resistance of the Mg-0.6Gd and Mg-0.4Dy alloys decreased with increasing annealing temperature due to an increase in grain size while the corrosion resistance of the Mg-1.4Nd alloy was improved after annealing at 450 °C due to precipitation and texture weakening.

Microstructures and Tensile Properties of New Mg–0.9Zn–0.2Mn–0.5RE Alloys via Different Al Additions

Effects of Al content on the microstructure and tensile properties of Mg–0.9Zn–0.2Mn–0.5RE (0.2Sm + 0.3La) alloy have been systematically investigated. In the as‐cast Mg–0.9Zn–0.2Mn–0.5RE alloy, intermetallic compounds are identified as Mg41Sm5, Mg12La, and Mg12(La, Sm) phases, while when Al is added, new Mg17Al12 and Al11(La, Sm)3 phase is formed instead of Mg12(La, Sm) phase. As Al content increases, Al11(La, Sm)3 phase increases and the morphology changes from a bright needle to a short rod in the as‐cast alloys. Al11(La, Sm)3 phase is broken and characterized as polygonal and rod shapes in as‐extruded alloys, and gradually increases in size and segregation as Al content increases, resulting in an increase in the ultimate strength and fluctuation of the average grain size, yield strength, and elongation. It should be noted that the as‐extruded alloy has good elongation (A ≈ 25.3%) with 3% Al content and good tensile strength (280 MPa ≤ Rm ≤ 300 MPa) with 6% and 9% Al content. Besides, the as‐extruded Mg–0.9Zn–0.2Mn–0.5RE–3Al alloy shows outstanding ductility due to the weakened texture of DRXed and sub‐structured grains and the high SF value in pyramidal <c + a> slip and basal <a> slip.

An experimental investigation on the influence of Sn addition and aging time on the mechanical and micro structural properties of AZ80-1.2RE magnesium alloy

This study investigated the effect of tin (0, 6, and 9 wt%) and aging time (0, 16, 24, and 32 hrs) on the microstructure and mechanical properties of the AZ80-1.2RE Mg alloy. The results obtained indicate that the addition of Sn improved the mechanical properties. For the AZ80-1.2RE alloy, upon Sn addition, strength of 195 MPa and percentage elongation of 7.6 are observed to be found at 6 wt% Sn, which is attributed to the precipitates of Al2RE, Mg2Sn, and Mg-Sn-RE phases. After heat treatment and aging, the properties of the casted alloys were found to be affected. As aging time increases, small precipitates are observed to be dissolved in primary Mg phase, due to which the properties are found to be decreased from the as-cast condition to aging at 16 hours. The strength of the 6wt% Sn alloy decreased due to the high stress concentration at the large precipitate site during aging from 16 hours to 24 hours and then increased due to the grain boundary strengthening effect at the 32-hour aging time.

Deformation behavior of the Mg–Zn–Zr–Nd–Gd alloy

Gd and Nd added Mg–Rare Earth (Mg–RE) alloys have attracted high-temperature applications due to their excellent combinations of high specific strength, high specific stiffness, good damping capacity, and better creep life. Despite these advantages, such Mg–RE alloys have attracted applications only in the cast form, owing to the difficulty in hot workability. Therefore, to understand the hot deformation behavior of Mg–Zn–Zr–Nd–Gd alloy, the present study correlates the results of hot compression studies with microstructure and texture. Serrated flow behavior is observed due to the dynamic strain aging. Maximum strain rate sensitivity is achieved between 580 K–650 K at lower strain rates 0.001 s−1–0.01 s−1. Dynamic recovery is predominantly active within this range of temperature and strain rate. Dynamic precipitation produces ultra-fine precipitates and leads to the suppression of dynamic recrystallization behavior. All deformed samples develop a relatively weak basal texture with the [0 0 0 1] axis parallel to the compression direction.

First–principles study of β′ phase in Mg–RE alloys

Resource conservation and environmental protection have become a priority development trend of rail transit. As magnesium alloy is the most effective lightweight material for its low density, high strength, and strong shock absorption, its large–scale application in rail vehicles contributes to lightweight, energy saving, and emission reduction. It is imperative to vigorously develop magnesium alloy with better properties, which may be closely related to its precipitate phases. However, research on the mechanical properties of β′ phase of different Mg–RE alloys is still insufficient. Therefore, the structure of β′ phase in Mg–RE (RE = Y, Gd, Tb, or Dy) alloys is constructed and its formation energies, electronic structures, elastic moduli, and elastic anisotropy were calculated by the first–principles method in this paper. The calculation results of formation enthalpy and elastic constants verify that these four alloys (Mg–Y, Mg–Gd, Mg–Tb, and Mg–Dy) are thermodynamically and mechanically stable. Moreover, the calculations of elastic modulus demonstrate that with RE addition, the elastic modulus are obviously improved, especially in Young's modulus which improvs from 9 to 18 GPa. Vickers hardness of β′ phase in Mg–RE alloys is calculated by the elastic moduli, which shows that Mg–RE alloys exhibit better hardness than that of α–Mg. The elastic anisotropy for each Mg–RE alloy is characterized by elastic anisotropic factors, three–dimensional views and projections of bulk, shear, and Young's moduli. The degree of anisotropy of elastic modulus are as follows: β′–Mg7Tb > β′–Mg7Y > β′–Mg7Gd > β′–Mg7Dy. The density of states and electron localization function indicate that strong metallic bonds forming between RE atoms and their neighbouring Mg atoms make contributions to their better mechanical properties. The Abovementioned results will provide beneficial data references for the Mg alloy design and characterization.

Effect of overheating treatment on morphological evolution of highly undercooled Al–70%Si-0.5%RE alloys

The effect of overheating on the morphological evolution of primary silicon in undercooled Al–70%Si-0.5%RE alloys was investigated by observing and recording their growth processes and then analyzing the as-solidified microstructure. Investigations revealed that an increase in the overheating and undercooling temperatures, transforms the primary silicon's growth morphology from dendrite with several long and thin branches to a blocky shape and then to equiaxed grains as the silicon atom clusters disappear. In addition, we observed that, in contrast to previously reported and theoretically predicted critical undercooling promoting morphology transition, the critical undercooling actually deceased the transformation from dendrite to blocky shape and then to equiaxed grains.

Designing new low alloyed Mg—RE alloys with high strength and ductility via high-speed extrusion

Designing new low alloyed Mg—RE alloys with high strength and ductility via high-speed extrusion

Investigation of Ti/Al2O3 + TiO2 and Ti + TiO2/Al2O3 + TiO2 hybrid coatings as protection of ultra-light Mg–(Li)–Al–RE alloys against corrosion

Low corrosion resistance is a significant problem of magnesium alloys, particularly ultra-light magnesium-lithium alloys. Surface treatment is one way to improve their corrosion resistance. The paper presents the results of tests of Ti/Al2O3 + TiO2 and Ti + TiO2/Al2O3 + TiO2 coatings obtained in a hybrid process combining PVD and ALD methods and ALD coating of Al2O3 + TiO2 type obtained on AE42 (Mg–4Li–2RE) and LAE442 (Mg–4Li–4Al–2RE). Structural studies were performed using scanning and transmission electron microscopy (SEM and TEM), atomic force microscopy and EDS and XPS spectroscopic methods. Potentiodynamic tests and electrochemical impedance spectroscopy EIS in 0.05 M NaCl solution were performed to determine the electrochemical properties of the tested materials. Moreover, tests of surface wettability and tribological properties using the ball-on-disc method were performed. Based on the analysis of anodic polarisation curves and Tafel analysis, it was found that the Ti + TiO2/Al2O3 + TiO2 coating showed the best potentiodynamic properties on both substrates. In particular, on the magnesium-lithium substrate, the value of the polarisation resistance of this hybrid coating is Rpol = 14 × 103 Ω × cm2, and the value of the corrosion current is jcorr = 0.4 µA/cm2. For the uncoated LAE442 substrate, the polarisation resistance is Rpol = 1.05 × 103 Ω × cm2, and the corrosion current value is jcorr = 5.49 µA/cm2. This improvement is due to the synergistic effect of the combined PVD and ALD technologies. The study confirmed the impact of hybrid coatings on improving the anti-corrosion and tribological properties of ultra-light magnesium alloys.

Effects of rare-earth elements on twinning deformation of Al alloys from first-principles calculations

Effects of rare-earth (RE = Ce, Dy, Er, Ho, La, Tb, and Yb) elements on twinning deformation of Al alloys are studied using first-principles calculations. The influence rules of RE atoms doped at the first nearest neighbor layer on the generalized planar-fault energy curves are analyzed, and the interaction energies of RE atoms in various atomic layers of stacking fault configurations are studied. On the basis of the improved twinning criterion formula and uniform distribution model, the influence rules of RE solute concentration on twinnability at the crack tip, at the grain boundary, and inside the grain of Al alloys are further analyzed. Results show that RE elements can evidently decrease the minimum energy barriers of dislocation nucleation and motion, and La and Ce atoms have significant effects on promoting dislocation nucleation and motion. Ce and La atoms can promote twinning deformation at the crack tip. Except for the La atom, the remaining RE atoms inhibit twinning deformation at the grain boundaries, and La atom at high concentrations is beneficial to promote twinning deformation at the grain boundaries. RE atoms (Dy, Er, Ho, La, Tb, and Yb) for twinning deformation inside Al alloy grains exhibit slight effect. Nevertheless, the Ce atom can greatly promote twinning deformation inside the grains when the solute concentration is in the range of 5%–7.1%, and the twinning ability decreases with the increase in solute concentration again. This work takes the lead in revealing the mechanism of twinning deformation by considering the interactions between RE atoms and generalized faults, which provides valuable guidance for exploiting high-performance Al–RE alloys.

Short- and long-term corrosion behavior of carbonate apatite-coated Mg-4mass% Y-3mass% RE alloy in cell culture medium

Osteoclast responsive carbonate apatite (CAp) coatings with different carbonate content rates and non-bioabsorbable hydroxyapatite (HAp) coating were formed on Mg-4mass% Y-3mass% rare earth (WE43) alloy. Electrochemical impedance spectroscopy measurement in a cell culture medium was performed for 6 h and 10 weeks, and the corrosion morphology was observed using a scanning electron microscope. Coating layer resistance of the CAp-coated specimens for 6 h was 104 Ωcm2 which was higher than 2 × 103 Ωcm2 of the HAp-coated specimen. Mean polarization resistance for the initial 4 weeks for the former was 4 × 104–7.5 × 104 Ωcm2 which was higher than 2 × 104 Ωcm2 of the latter.

Impression Creep Behavior of an Mg–Zn–RE Alloy at Elevated Temperatures

Impression Creep Behavior of an Mg–Zn–RE Alloy at Elevated Temperatures