Search Results (70)

In the medical field, magnesium (Mg) alloys have been widely used due to their excellent antibacterial properties and biodegradability. However, in the marine environment, the antibacterial effect may be greatly attenuated, and consequently, microorganisms in the ocean are likely to adhere to the surface of Mg alloys, resulting in biocorrosion damage, which is really troublesome in the maritime industry and can even be disastrous to the navy. Currently, there is a lack of research on the biocorrosion of Mg alloys that may find important applications in marine engineering. In this paper, the biocorrosion mechanism of the Mg alloy Mg-3Nd-2Gd-Zn-Zr caused by Chlorella vulgaris (C. vulgaris), a typical marine microalga, was studied. The results showed that the biomineralization process in the artificial seawater containing a low concentration of C. vulgaris cells was accelerated compared with that in the abiotic artificial seawater, leading to the deposition of CaCO₃ on the surface to inhibit the localized corrosion of the Mg alloy, whereas a high concentration of C. vulgaris cells produced a high content of organic acids at some sites through photosynthesis to significantly accelerate the surface film rupture at some sites and severe localized corrosion there, but meanwhile, it resulted in the formation of a more protective biomineralized film in the other areas to greatly alleviate the corrosion. The contradictory biocorrosion behaviors on the Mg-3Nd-2Gd-Zn-Zr alloy induced by C. vulgaris were finally explained by a mechanism proposed in the paper. Full article

This study presents a comparative analysis of the influence of Ce-Gd and Gd-Y additions on the microstructural evolution, mechanical properties, and electrochemical behavior of extruded Mg-3Zn-Mn-Ca alloy rods. Despite the frequent incorporation of Gd, Y, and Ce as alloying elements in magnesium alloys, the systematic examination of their combined effects on Mg-Zn alloys has been limited. Our findings reveal that both Gd-Ce and Gd-Y additions significantly enhance the mechanical properties of Mg-3Zn-Mn-Ca alloy, although through differing mechanisms. Specifically, the Mg-3Zn-1Mn-0.5Ca-1Gd-0.5Ce(ZMXE3101(GdCe)) alloy exhibited a yield strength of 304.5 MPa and an elongation of 15%, achieved through dynamic recrystallization and enhanced basal texture. The grain refinement and texture strengthening resulting from the coarse second-phase particles formed by Ce-Gd played a significant role in increasing the yield strength. In contrast, the Mg-3Zn-1Mn-0.5Ca-1Gd-0.5Y (ZMXE3101(GdY)) alloy demonstrated a yield strength of 305 MPa and an elongation of 20%. The finer grains and elongated unrecrystallized grains formed by Gd-Y contributed to the elevation in yield strength. While the ductility of this alloy was slightly lower than that of Mg-3Zn-Mn-Ca without rare earth additions, it still exhibited commendable overall mechanical properties. The electrochemical test results indicate that the addition of both Gd-Ce and Gd-Y enhances the corrosion current density of Mg-3Zn-Mn-Ca alloy, attributable to the generation of numerous rare earth phase particles that function as cathodes. Compared to the ZMXE3101(GdY) alloy, ZMXE3101(GdCe) exhibits a higher equilibrium potential and significantly lower corrosion current density. This is due to the formation of a protective film during the corrosion process by Gd-Ce. Full article

In this study, the electrochemical performance and discharge behavior of Mg-Li-Zn-Gd alloys with α-Mg and β-Li-based anode material are investigated, with the aim to improve the anode performance of Mg-air batteries. The experimental anode alloys with detailed Mg-8Li-xZn-yGd (x = 1, 2, 3; y = 1, 2, 3 wt.%) components are prepared, and extrusion deformation is carried out on these alloys. Simultaneously, scanning electron microscope (SEM), X-ray diffractometer (XRD), electrochemical workstation, and constant current discharge systems are applied for microstructure characterization, corrosion, and discharge performance testing. The results show that the experimental alloys are composed of an α-Mg and β-Li dual matrix, with W-Mg₃Gd₂Zn₃, Mg₃Gd, and MgLiZn second phases. Meanwhile, extrusion deformation promotes the recrystallization process through the particle-induced nucleation mechanism. The corrosion resistance is improved with the increasing Zn/Gd ratio, and the extruded Mg-8Li-2Zn-1Gd (LZG821) alloy exhibits the optimum corrosion resistance, with a corrosion rate of 0.493 mm·year⁻¹. In addition, the extruded Mg-8Li-1Zn-1Gd (LZG811) alloy has the optimal discharge performance, with a discharge specific capacity of 1371.04 mA·g⁻¹ at a current density of 40 mA∙cm⁻², and its anode efficiency reaches nearly 70%. The poorer discharge properties of the Mg-8Li-2Zn-1Gd (LZG821) and Mg-8Li-2Zn-3Gd (LZG823) alloys are attributed to their refined grains, which could bring severe intergranular corrosion while increasing the grain boundary density. Full article

The tension-compression yield asymmetry caused by the strengthening of Mg-Zn-Gd-Zr alloy due to extrusion deformation is an important issue that must be addressed in its application. In this study, the effects of loading direction on the tensile and compressive mechanical behaviors of Mg-5Zn-2Gd-0.2Zr alloy were systematically investigated. As the loading angle (the angle between the loading direction and the extrusion direction) increases from 0° to 30°, 45°, 60° and 90°, the tensile yield strength decreases more significantly than the compressive yield strength. Consequently, the tension-compression yield asymmetry is gradually improved. Additionally, the ultimate compressive strength decreases more markedly than the ultimate tensile strength with the increment of the loading angle. In tensile tests conducted at 0°, 30° and 45°, two distinct stages of decreasing strain hardening rates are typically observed. For the 60° and 90° tensile tests, one unusual ascending stage of strain hardening rate is observed. For all compressive tests, three stages of strain hardening are consistently noted; however, the increment in strain hardening rate caused by {10–12} extension twinning decreases with the increasing loading angle. A model combining loading angle and Schmid factor distribution was established. The calculated results indicate that the dominant deformation modes during the yielding process also vary significantly with the loading conditions. This clarification highlights the differences in yield strength variations between tension and compression. Finally, an analysis of the plane trace and crack propagation direction near the fracture surface reveals the fracture mechanisms associated with tensile and compressive tests at different loading directions. This study promotes understanding of the mechanical behaviors of Mg-5Zn-2Gd-0.2Zr alloy under different loading directions, and helps to thoroughly elucidate the anisotropic effects of texture on the mechanical properties of magnesium alloys. Full article

Rare-earth magnesium alloys exhibit higher comprehensive mechanical properties compared to other series of magnesium alloys, effectively expanding their applications in aerospace, weapons, and other fields. In this work, the tensile strength, yield strength, and elongation of a Mg-Gd-Y-Zn-Zr rare-earth magnesium alloy under different process conditions were determined, and a large number of microstructure observations and analyses were carried out for the tensile specimens; a prediction model of the corresponding mechanical properties was established by using a convolutional neural network (CNN), in which the metallographic diagram of the rare-earth magnesium alloy was taken as the input, and the corresponding tensile strength, yield strength, elongation, and three mechanical properties were taken as the output. The stochastic gradient descent (SGD) algorithm was used for parameter optimization and experimental validation, and the results showed that the average relative errors of the tensile strength and yield strength prediction results were 1.90% and 3.14%, respectively, which were smaller than the expected error of 5%. Full article

Mg-Gd-Y-Zn-Mn (MVWZ842) is a kind of high rare earth magnesium alloy with high strength, high toughness and multi-scale strengthening mechanisms. After heat treatment, the maximum tensile strength of MVWZ842 alloy is more than 550 MPa, and the elongation is more than 5%. Because of its great mechanical properties, MVWZ842 has broad application potential in aerospace and rail transit. However, the addition of high rare earth elements makes the deformation resistance of MVWZ842 alloy increase to some extent. This leads to the difficulty of direct plastic processing forming and large structural part shaping. Friction stir welding (FSW) is a convenient fast solid-state joining technology. When FSW is used to weld MVWZ842 alloy, small workpieces can be joined into a large one to avoid the problem that large workpieces are difficult to form. In this work, a high-quality joint of MVWZ842 alloy was achieved by FSW. The microstructure and properties of this high-strength magnesium alloy after friction stir welding were studied. There was a prominent onion ring characteristic in the nugget zone. After the base was welded, the stacking fault structure precipitated in the grain. There were a lot of broken long period stacking order (LPSO) phases on the retreating side of the nugget zone, which brought the effect of precipitation strengthening. Nano-α-Mn and the broken second phase dispersed in the matrix in the nugget zone, which made the grains refine. A relatively complete dynamic recrystallization occurred in the nugget zone, and the grains were refined. The welding coefficient of the welded joint exceeded 95%, and the hardness of the weld nugget zone was higher than that of the base. There were a series of strengthening mechanisms in the joint, mainly fine grain strengthening, second phase strengthening and solid solution strengthening. Full article

In this study, we prepared Mg-9Gd-2Nd-0.5Zr, referred to as alloy I, and Mg-9Gd-2Nd-1.5Zn-0.5Zr, referred to as alloy II. The effects of a long-period stacking ordered (LPSO) phase induced by Zn addition on the high-temperature mechanical properties and fracture morphology of alloy I and alloy II at different temperatures (25 °C, 200 °C, 225 °C, and 250 °C) were studied using optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The results indicate that Mg₅RE at the crystal boundary of the as-cast alloy I transformed into (MgZn)₃RE (as-cast alloy II) by the addition of Zn. After solid solution treatment, the secondary phase in alloy I completely disappeared, and there were still residual secondary phases in block-like and needle-like structures in alloy II, while layered LPSO phases precipitated in the matrix. During the high-temperature tensile test, the yield and tensile strength of alloy I decreased significantly with the increase in temperature, while the elongation increased. Compared to alloy I, the yield strength of alloy II with an LPSO phase showed an increasing trend at 25 °C~200 °C and then decreased when the temperature reached around 250 °C. The thermal stability was significantly enhanced, and the elongation was also higher than that of alloy I. As the temperature increased, the fracture surface of alloy I showed increased folding, bending of scratches, and crack enlargement. However, the fracture surface of alloy II remained largely unchanged, with only minor wrinkles and cracks appearing at temperatures reaching 250 °C. Full article

Magnesium and its alloys are attractive temporary implants due to their biocompatibility and biodegradability. Moreover, Mg has good mechanical and osteoinductive properties. But magnesium and Mg alloys have one significant disadvantage: poor corrosion resistance in a physiological environment. Hence, a deposition of various layers on the surface of Mg alloys seems to be a good idea. The purpose of the article is to analyze the structure and morphology of two MgCa2Zn1 and MgCa2Zn1Gd3 alloys coated by SnO₂ ALD (atomic layer deposition) films of various thickness. The studies were performed using scanning electron microscopy (SEM), X-ray fluorescence (XRF), and an X-ray diffractometer. The corrosion activity of the thin films and substrate alloys in a chloride-rich Ringer’s solution at 37 °C was also observed. The corrosion tests that include electrochemical, immersion measurements, and electrochemical impedance spectroscopy (EIS) were evaluated. The results indicated that SnO₂ had a heterogeneous crystal structure. The surfaces of the thin films were rough with visible pores. The corrosion resistance of SnO₂ measured in all corrosion tests was higher for the thicker films. The observations of corrosion products after immersion tests indicated that they were lamellar-shaped and mainly contained Mg, O, Ca, and Cl in a lower concentration. Full article

A high strength and ductile Mg-Gd-Y-Zn-Zr alloy was designed and fabricated. The local strain evolution of the alloys during plastic deformation was analyzed using high-resolution digital image correlation (DIC). The results showed that the β particles, nano-sized γ’ phases, and LPSO phases were distributed in the as-extruded alloy and a bimodal microstructure was exhibited, including elongated un-dynamic recrystallized grains and fine dynamic recrystallized grains. With increasing extrusion ratio, the grain size remained, with the volume fraction of dynamic recrystallization of the as-extruded alloy increasing from 30% to 75%, and the as-extruded alloy exhibited a high strength-ductility synergy, which is attributed to the grain refinement, extensive β particles, and elongated block-shaped LPSO phases. The strain evolution analysis showed that a strain-transfer from un-DRXed regions to adjacent DRXed regions and LPSO phases can promote uniform plastic deformation, which tends to improve the ductility of the alloy. Full article

The exploration of the relationship between process parameters and grain evolution during the thermal deformation of rare-earth magnesium alloys using simulation software has significant implications for enhancing research and development efficiency and advancing the large-scale engineering application of high-performance rare-earth magnesium alloys. Through single-pass hot compression experiments, this study obtained high-temperature flow stress curves for rare-earth magnesium alloys, analyzing the variation patterns of these curves and the softening mechanism of the materials. Drawing on physical metallurgical theories, such as the evolution of dislocation density during dynamic recrystallization, recrystallization nucleation, and grain growth, the authors of this paper establish a cellular automaton model to simulate the dynamic recrystallization process by tracking the sole internal variable—the evolution of dislocation density within cells. This model was developed through the secondary development of the DEFORM-3D finite element software. The results indicate that the model established in this study accurately simulates the evolution process of grain growth during heat treatment and the dynamic recrystallization microstructure during the thermal deformation of rare-earth magnesium alloys. The simulated results align well with relevant theories and metallographic experimental results, enabling the simulation of the dynamic recrystallization microstructure and grain size prediction during the deformation process of rare-earth magnesium alloys. Full article

A suitable heat treatment in the Mg₉₇Gd₂Zn₁ (at.%) alloy in the as-cast condition results, after extrusion at high temperature, in a two-phase lamellar microstructure consisting of magnesium grains with thin lamellar shape precipitates and long fibers of the 14H-Long-Period Stacking Ordered (LPSO) phase elongated in the extrusion direction. The magnesium matrix is not fully recrystallized and highly oriented coarse non-dynamically recrystallized (non-DRXed) grains (17% volume fraction) elongated along the extrusion direction remain in the material. The deformation mechanisms of the extruded alloy have been studied measuring the evolution of the internal strains during in situ tension and compression tests using synchrotron diffraction radiation. The data demonstrate that the macroscopic yield stress is governed by the activation of the basal slip system in the randomly oriented equiaxed dynamic recrystallized (DRXed) grains. Non-DRXed grains, due to their strong texture, are favored oriented for the activation of tensile twinning. However, the presence of lamellar-shape precipitates strongly delays the propagation of lenticular thin twins through these highly oriented grains and they have no effect on the onset of the plastic deformation. Therefore, the tension–compression asymmetry is low since the plasticity mechanism is independent of the stress mode. Full article

A new heat source combination, consisting of a uniform body heat source and a tilted double ellipsoidal heat source, has been developed for cold metal transfer (CMT) wire-arc additive manufacturing of Mg-Gd-Y-Zn-Zr alloy. Simulations were conducted to analyze the temperature field and stress distribution during the process. The optimal combination of feeding speed and welding speed was found to be 8 m/min and 8 mm/s, respectively, resulting in the lowest thermal accumulation and residual stress. Z-axis residual stress was identified as the main component of residual stress. Electron Backscatter Diffraction (EBSD) testing showed weak texture strength, and Kernel Average Misorientation (KAM) analysis revealed that the 1st layer had the highest residual stress, while the 11th layer had higher residual stress than the 6th layer. Microhardness in the 1st, 11th, and 6th layers varies due to residual stress impacts on dislocation density. Higher residual stress increases dislocation density, raising microhardness in components. The experimental results were highly consistent with the simulated results. Full article

Mg alloys with excellent high-temperature mechanical properties are urgently desired to meet the design requirements of new-generation aircraft. Herein, novel cast Mg-10Gd-2Y-0.4Zn-0.2Ca-0.5Zr-xAg alloys were designed and prepared according to the advantages of multi-component alloying. The SEM and XRD results revealed that the as-cast microstructures contained α-Mg grains, β, and Zr-containing phase. As Ag rose from 0 wt.% to 2.0 wt.%, the grain size was refined from 40.7 μm to 33.5 μm, and the β phase significantly increased. The TEM observations revealed that the nano-scaled γ′ phase could be induced to precipitate in the α-Mg matrix by the addition of Ag. The stacking sequence of lamellar γ′ phases is ABCA. The multiple strengthening phases, including β phase, γ′ phases, and Zr-containing particles, were effectively tailored through alloying and synergistically enhanced the mechanical properties. The ultimate tensile strength increased from 154.0 ± 3.5 MPa to 231.0 ± 4.0 MPa at 548 K when Ag was added from 0 to 2.0 wt.%. Compared to the Ag-free alloy, the as-cast alloy containing 2.0 wt.% Ag exhibited a minor reduction in ultimate tensile strength (7.0 ± 4.0 MPa) from 498 K to 548 K. The excellent high-temperature performance of the newly developed Mg-RE-Ag alloy has great value in promoting the use of Mg alloys in aviation industries. Full article

In order to improve the corrosion resistance of Mg-3Gd-1Zn-0.4Zr (GZ31K) alloys for biomedical application, the alloy was micro-arc oxidation (MAO)-treated using silicate electrolyte system under various voltages (400 V, 425 V, 450 V, 475 V). The effects of voltage on the microstructure and corrosion properties of MAO coating were investigated via X-ray diffraction (XRD) and a scanning electron microscope (SEM) combined with an energy-dispersive spectrometer (EDS), X-ray photoelectron spectroscope (XPS), and electrochemical experiments. The results showed that, with the increase in voltage, the MAO coatings became thicker and the micropores on the MAO coating increased in diameter. The main phase compositions of the MAO coatings were MgO and Mg₂SiO₄. Potentiodynamic polarization curve results showed that MAO coatings could enhance corrosion resistances, where the corrosion current density decreased by six orders of magnitude and the corrosion potential of the specimens increased by 300 mV for the voltage of 450 V in the MAO treatment; nevertheless, the corrosion resistance rapidly deteriorated due to the creation of large micropores in the MAO coating, which provide a pathway for corrosive media when the voltage is 475 V. The electrochemical impedance spectroscopy results showed that MAO treatments could increase low-frequency modulus resistance and increase the corrosion resistance of Mg alloys. In addition, MAO-treated GZ31K alloys still exhibited uniform corrosion, which is desirable for biomedical applications. Full article

The Mg-(4-x)Nd-xGd-0.3Sr-0.2Zn-0.4Zr (x = 0, 1, 2, and 3 wt%, Gd/Nd = 0, 1/3, 1, and 3) alloys were hot extruded and then aged (T5). The friction and wear properties of the as-extruded and as-aged alloys were studied using a ball-on-disk wear testing machine and a scanning electron microscope to reveal the impacts of the Gd/Nd ratio and aging treatment. The results show that the friction coefficient of the as-extruded alloys increases first and then decreases with increasing Gd/Nd ratio. After aging, the friction coefficient of the alloys decreases slightly. The Gd/Nd ratio has no significant effect on the wear rate of the as-extruded alloys, and the wear rate decreases first and then increases with the increase in the Gd/Nd ratio for the as-aged alloys. The T5 alloy with a Gd/Nd ratio of 1/3 has the best wear resistance. The wear mechanisms of alloys mainly include abrasive wear, oxidation wear, and delamination wear. Full article