La Alloy Research Articles

Laser surface melting of Al–Co–rare earth (Ce–La) alloys for improving corrosion resistance

The development of Al-RE (rare earth) alloys is primarily attributed to their excellent thermal stability, corrosion resistance, and tunable properties based on Co and Ce elements. Considering the need for a high critical cooling rate, it is a challenging phenomenon to develop fine and homogeneous Al-TM-RE alloy in bulk form. Therefore, it is a suitable alternative to use surface modification techniques to produce refined and homogenized coatings or thin films for achieving better corrosion resistance in the surface. In this study, the surface of two types of Al–Co–Ce–La alloys were treated by the Laser Surface Melting method with two different laser scanning speeds, and the effects of this process on the microstructure and corrosion properties were evaluated compared to the as-cast samples. The microstructural characteristics, chemical composition, phase change, and corrosion properties were evaluated. The results indicated that the particle sizes and the inter-particle distance in the Al matrix decrease significantly. The microstructure of the LSM samples are much more refined and homogenized, Compared to the as-cast crystalline material. The depth of microstructural affected zone by the laser surface process increased to an acceptable level (590 µm). No trace of microcrack formation and distortion were observed in the LSM samples. The decreased linear line energy from 83.6 to 41.8 j/mm led to the reduced interaction time and decreased amount of crystalline phases, thereby increasing the probability of amorphous structure. The best corrosion properties were obtained in the laser-treated Al83.0Co10.0-Ce4.3-La2.7 alloy with a scanning speed of 20 mm/s.

Microstructure of Al–Mg–Si–La alloy under pulsed magnetic field treatment during solidification

The grains refinement and secondary phase modification mechanism of Al–Mg–Si–La alloy under pulsed magnetic field during solidification were studied in detail. With application of pulsed magnetic field, the microstructure of Al–Mg–Si–La alloy consists of fine and equiaxed grains. Meanwhile, the smaller size of Mg2Si homogeneously dispersed in α-Al grains, and the number of AlFeSi and LaAlSi phase obviously decreased compared with the ones without pulsed magnetic field treatment. The cluster nucleation at the liquid region during early solidification stage is dominant reason for grains refinement in Al–Mg–Si–La alloy under pulsed magnetic field. Theoretical calculation indicated that pulsed magnetic field provides maximum energy in the alloy melt at about 760°C, which decreased the critical radius and energy barrier for nucleation.

Effect of La addition on microstructure, mechanical behavior, strengthening and toughening mechanisms of cast Mg-Gd-Zn alloy

High strength cast Mg-RE (magnesium-rare earth) alloys usually show a poor balance between strength and ductility, typically high strength with low ductility. Grain coarsening during solution treatment is one of the reasons for the reduced ductility. La element has very limited solubility in Mg and the La-containing second-phase is expected to pin the grain boundaries and restrict the significant grain coarsening during solution treatment. Therefore, different amounts of La addition are introduced to the Mg-Gd-Zn casting alloy and the microstructure and mechanical properties are systematically studied. The addition of La results in the formation of the Mg12La second-phase along the grain boundaries during solution treatment, significantly increasing the number density of the β’ precipitates while slightly reducing their sizes. The Mg12La phase along the grain boundaries restricts grain coarsening, resulting in very low grain coarsening rates in the La-containing alloys. Compared with high strength cast Mg-RE alloys in literature, the present La-containing alloys indicate better balance between strength and ductility. The 0.4 La alloy exhibits the highest yield strength (YS) of 247 MPa and ultimate tensile strength (UTS) of 397 MPa with moderate elongation (El) of 5.8% in the under-aged condition; while the 0.2 La alloy with the highest product of strength and elongation (PSE) of 4.63 GPa·% presents a good combination of high strength and outstanding elongation (YS: 245 MPa; UTS: 383 MPa; El: 12.1%) in the peak-aged condition. Micro-alloying with La element is expected to be an effective strategy to improve the strength and ductility of cast Mg alloys simultaneously.

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.

On Shapes and Orientations of Precipitation Strengthening Phases in an Aged Mg–La Alloy

On Shapes and Orientations of Precipitation Strengthening Phases in an Aged Mg–La Alloy

Insights into the local structure evolution and thermophysical properties of NaCl–KCl–MgCl2–LaCl3 melt driven by machine learning

The local structure evolution and thermophysical properties of the NaCl–KCl–MgCl2–LaCl3 melt were thoroughly understood, which facilitates the advancement and innovation of molten salt electrolytic production for Mg–La alloys.

Plasma-assisted cutting for impurity reconstruction of an as-cast cerium–lanthanum alloy

The high chemical activity and oxide impurities inside cerium–lanthanum (Ce–La) alloys make it difficult to achieve high surface finishing with diamond turning. Plasma-assisted cutting, in which the plasma is applied to regulate the longitudinal impurity distribution of the surface layer and improve its machinability in diamond turning, is proposed for machining as-cast Ce–La alloys. The effect of the rotational speed on built-up edge is discussed, and a surface with surface roughness of 6.5 nm in Sa is successfully achieved. Experimental results show that the machined modified alloy possesses good oxidation resistance, benefiting various applications in green energy.

The hot deformation behavior and microstructural evolution of as-cast Mg–2Zn–0.5Mn–0.2Ca–0.3Nd–0.7La alloy

The microstructure and texture evolutions of the Mg–2Zn–0.5Mn–0.2Ca–0.3Nd–0.7La alloy were investigated by hot compression tests, which carried out in the temperatures range of 250–400 °C and strain rates range of 0.001–1 s−1. The thermal deformation behavior of the alloy was reflected by the hyperbolic sine function relationship, which was applicable to all stresses conditions due to the calculated value of α∗σp was 1.0. The thermal processing map based upon the dynamic material model was built. In addition, the suitable and unsuitable hot working regions were analyzed combined with microstructures. The results show that the dynamic recrystallization (DRX) mechanism of the hot compression deformation microstructure of the alloy was discontinuous dynamic recrystallization (DDRX). There were plenty of extension twins in some coarse deformed grains and these twins form a new <0001>//TD texture, which led to the weakening the <0001>//CD texture.

Research on microstructure and mechanical properties of die casting Mg-4Al-1Si-3RE (Ce, La) and AS41 alloys

Mg-4Al-1Si-3Ce (ASCe), Mg-4Al-1Si-3La (ASLa), Mg-4Al-1Si-1.5Ce-1.5La (ASCeLa), and Mg-4Al-1Si (AS41) alloys were prepared by die-casting process, and the microstructure, tensile mechanical properties, friction and wear behavior and wear mechanism under different loads were systematically analyzed. It was found that die-casting Mg-4Al-1Si-3RE (Ce, La) (ASRE) alloys mainly contain three kinds of rare earth phases: lamellar REMg2Si2, rod-shaped Al11RE3, and granular Al2RE. Besides, a finer CeLaMg4Si4 phase exists in the ASCeLa alloy, which has a semi-coherent interface relationship with Mg2Si. Moreover, the Al11Ce3 phase in the ASCe alloy was not only attached to the end of the Mg2Si phase, but also perpendicular to the Mg2Si, thus hindering the growth of the Mg2Si phase. Among three rare earth alloys, the ASCeLa alloy possesses the smallest grain size of about 9 µm. In addition, its hardness, ultimate tensile strength, yield strength and elongation reach 85.55HV, 263 MPa, 167 MPa, and 12.03%, respectively, which are increased by 22.9%, 23.7% and 64.6% compared with typical die-casting AS41 alloy, respectively. At the same time, under the materials and test conditions given in this paper, compared with AS41 alloy, ASRE alloys have better friction and wear properties. Under the low load, the presence of rare earth elements improves wear resistance and prevents a drastic increase in local frictional heat. As the load increases, the amount of the wear debris increases, while the coefficient of friction decreases. When the load increases from 40 N to 120 N, the wear mechanism of ASRE alloys changes to delamination wear. Among three rare earth alloys, the ASCeLa alloy has the best friction and wear performance, which is attributed to the dispersion of the second phases with high hardness and high melting point along the grain boundaries and within the grains, solid solution strengthening effect of mixed rare earth elements and grain refinement. This research helps reveal the strengthening mechanism of Ce and La elements, and provides a reference for the design of high-strength die-casting magnesium alloys.

Bimodal microstructure evolution and strength-ductility co-enhancement of hot-extruded Al–La–Mg–Mn alloy

Novel heat-resistant Al-(La, Ce) alloys are strengthened via alloying with high Mg; however, their ductility deteriorates due to the formation of coarse intermetallics. In this work, a conventional hot extrusion process was used to refine the microstructures of Al–La alloy with a high Mg addition. Bimodal intermetallic and grain structures were observed in the as-extruded alloy. Of note, the coarse intermetallics were decorated with high-density microcracks. The as-extruded alloy achieved a good balance between strength and ductility, exhibiting a high ultimate tensile strength (360 ± 2 MPa) and good elongation (9.6 ± 0.6%). The high strength was mainly attributed to the strong strain-hardening ability and the load-transfer effect. Good elongation arises from the propagation of pre-existing microcracks, microstructure refinement, and increased strain-hardening ability. These findings reveal that a combination of pre-existing microcracks and a matrix with strong strain-hardening ability is a promising feature for microstructural design with increased ductility.

Microstructure control and its observation of rapid solidification Cu–La alloy for the development of fluoride-ion batteries

We report on the microstructure of Cu-La alloys, which is a candidate material for the electrode of fluoride-ion battery, prepared by the rapid solidification method. The Cu-La alloys near eutectic point (24.5at%La) were quenched at different cooling speed to obtain optimized lamellar microstructure. The cross-section of the Cu-24.5at%La alloy exhibited a lamellar microstructure, in which the Cu-rich and La-rich phases were well proportioned. A hexagonal Cu5La phase with a space group P6/mmm was confirmed in the Cu-enriched areas, along with tetragonal Cu4La particles with an I4̅m2 and hexagonal Cu2La with the P6/mmm. Furthermore, different cooling rate during solidification were applied by changing the wheel rotation speed of the device. The higher the rotation speed, the faster the cooling rate, and the finer the microstructure. The width of each layer in the microstructure was approximately 100 nm.

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

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

Thermodynamic and kinetic analysis of ternary intermetallics formation in Al–Cu–La alloy

The thermodynamic and kinetic analysis of rare earth (RE) intermetallics formation in Al–Cu–La alloy was carried out in this study. The formation enthalpy, excess entropy, excess Gibbs free-energy and activity of each component of Al–Cu–La ternary alloy were calculated combining Miedema model with Toop model. The calculated results show that the formation enthalpy, excess entropy and excess Gibbs free-energy of Al–Cu–La ternary alloy are all negative in the whole alloy composition range. The activities of Al, Cu and La are all tiny in the central zone of composition triangle of Al–Cu–La ternary alloy, indicating that Al, Cu and La components are easy to form ternary intermetallics. Moreover, the parabolic growth kinetics equation of RE intermetallics was derived integrating the Fick's second law with the mass balance law. According to the parabolic growth rate, the thickness of the RE intermetallics increases in proportion to the square root of the diffusion time.

Study on the Occurrence State of Lanthanum in Rust Layer and Mechanism of Its Influence on Invasion State of Corrosion Atoms

Rare earth elements have unique outer electronic structure, variable valence, and strong chemical activity; however, their occurrence state in the rust layer and influence on the invasion state of corrosion atoms are still unclear. Herein, using a combination of experiment and first‐principles calculation, the occurrence state of La in the rust layer of low‐alloy high strength steel, the phase composition, compactness and stability of the rust layer, and the invasion state of corrosion atoms before and after La alloying are studied. The results show that La exists in the corrosion products in the form of a solute atom. La increases the concentration of corrosion‐resistant elements Cr and Mo in the rust layer but does not change the phase composition. La is conducive to stabilizing Cl atoms in α‐FeOOH and β‐FeOOH, so as to protect the steel matrix from Cl. La atoms inhibit the dissolution of Cl atoms into γ‐FeOOH and Fe3O4 structures and hinder their formation.

Effect of La addition on semi-solid microstructure evolution of Mg-7Zn magnesium alloy

Semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys were prepared by semi-solid isothermal heat treatment. The effects of the La element on the as-cast and semi-solid microstructures of Mg-7Zn alloy were investigated. Meanwhile, the effects of isothermal temperature and holding time on the evolution of the semi-solid microstructure of Mg-7Zn-0.3La alloy were also studied. Results indicate that the addition of a small amount of La can significantly refine the as-cast and semi-solid microstructure. During the semi-solid thermal transformation, the size and shape factor of solid particles decrease at first and then increase with the increase of isothermal temperature and holding time. The semi-solid microstructure of Mg-7Zn-0.3La alloy obtained by holding at 605 °C for 30 min is the optimal. The average size of solid particles, shape factor, and solid fraction are 42 µm, 1.45 and 61.8%, respectively. At the same time, a comparative study on the coarsening process of particles in the semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys reveals that the addition of La effectively decreases the coarsening rate of solid particles and restricts the growth of solid particles.

Novel Mg-Ca-La alloys for guided bone regeneration: Mechanical performance, stress corrosion behavior and biocompatibility

Guided bone regeneration (GBR) is a therapeutic method that is used to augment deficient ridges before dental implantation. The non-absorbable membranes need secondary removal surgery, while absorbable collagen membranes fail while being applied to large bone defects because of their relatively low stiffness. The “ideal” membrane for use in GBR has yet to be developed. This study aims to develop and explore the feasibility of Mg-Ca-La alloys for application in GBR. Mg-0.2Ca-0.2La alloy exhibits fine microstructure and a good combination of tensile strength and ductility. Mg-0.2Ca-0.2La alloy is also capable of supporting the adhesion, proliferation and migration of human gingival fibroblasts, and shows good cytocompatibility on MC3T3-E1 cells. The GBR membranes usually need intraoperative bending or shaping to adapt the alveolar ridge. The additional effect of bending stress on magnesium-based materials must be considered due to a well-known issue, namely stress-corrosion cracking (SCC). The SCC results reveal that the bended Mg-0.2Ca-0.2La presents a uniform corrosion morphology with a corrosion rate of 0.09 mm/yr, which is 61% less than that of unstressed ones. Mg-0.2Ca-0.2La alloy possesses adequate strength and ductility, high biocompatibility and slow degradation under bending stress, contributing to adequate malleability and sustained spatial stability for membrane use.

Structure of Cast Nd–R–Fe–B (R = Pr, Ce, La) Alloys for Sintered Permanent Magnets

Structure of Cast Nd–R–Fe–B (R = Pr, Ce, La) Alloys for Sintered Permanent Magnets

Influence of the simultaneous processes of scale evaporation and reaction surface reduction on the oxidation kinetics of chromia-forming alloys doped with rare-earth elements

The high-temperature oxidation of FeCr(La) and Cr(Ce) alloys was studied by thermogravimetry. The kinetic dependence of the FeCr(La) mass change has a specific form due to the simultaneous occurrence of scale evaporation and reduction of the reaction surface. The latter is due to the formation of diffusion barriers from lanthanum chromite. The kinetic dependence of the mass change of Cr(Ce) has an identical form. Based on this identity, it was suggested that diffusion barriers can also exist in the Cr(Ce) alloy, as is the case for the FeCr(La) alloy.

La containing Mg alloy for enhanced corrosion at elevated temperatures in ethylene glycol media

A novel Mg alloy (Mg-10Dy-0.7La) was reported to have an excellent combination of corrosion and mechanical properties at room temperature. For its widespread applicability, particularly in the automotive sector, high-temperature corrosion investigation in cooling media is required. A combination of immersion test, potentiodynamic polarization and electrochemical impedance measurements were utilized to evaluate the corrosion behavior at different temperatures under ethylene glycol. The results suggested that Mg-10Dy-0.7La alloy has considerably enhanced corrosion resistance than AZ91 Mg alloy. This was attributed to higher activation energy and enhanced concentration of oxides (Dy2O3, La2O3, MgO and MgCO3) in former than that of latter.

Ameliorated microstructure and hydrogen absorption/desorption properties of novel Mg–Ni–La alloy doped with MWCNTs and Co nanoparticles

Based on the positive influence of carbon materials and transition metals, a new type of Mg-based composites with particle size of ∼800 nm has been designed by doping hydrogenated Mg–Ni–La alloy with multi-walled carbon nanotubes (MWCNTs) and/or Co nanoparticles. The microstructures, temperature related hydrogen absorption/desorption kinetics and dehydrogenation mechanisms are investigated in detail. The results demonstrate that MWCNTs and Co dispersedly distribute on the surface of Mg–Ni–La particles after high-energy ball milling due to powders’ repeated cold welding and tearing. The experimental samples exhibit improved hydrogen storage behaviors and the addition of MWCNTs and Co can further accelerate the de-/hydriding kinetics. For instance, the Mg–Ni–La–Co sample can absorb 3.63 wt% H2 within 40 min at 343 K. Dehydrogenation analyses demonstrate that the positive effect of MWCNTs is more obvious than that of Co nanoparticles for the experimental samples. The addition of MWCNTs and Co leads to the average dehydrogenation activation energy of experimental samples decreasing to 82.1 and 84.5 kJ mol−1, respectively, indicating a significant decrease of dehydrogenation energy barriers. In addition, analyses of dehydrogenation mechanisms indicate that the rate-limiting steps vary with the addition of MWCTNs and Co nanoparticles.