Mg-6 Wt Research Articles

Effect of I-phase formation on hydrogen embrittlement behaviour of as-cast Mg-8 wt%Li based alloys

By performing microstructural characterization, tensile testing and failure analysis, the effects of electrochemical H-charging on microstructure and mechanical behaviour of two as-cast Mg-8Li (in wt%) based alloys were investigated and compared. Due to the in-situ formation of I-phase, the failure elongation ratio for Mg-8Li-6Zn-1Y alloy was 31.2 % and its hydrogen embrittlement (HE) susceptibility was about 1/4 that of Mg-8Li alloy after H-charging for 24 h. Moreover, the preferential location of H-induced pores transferred from two matrix phases to I-phase/matrix eutectic pockets due to the preferential H absorption of I-phase, resulting in the higher HE resistance of Mg-8Li-6Zn-1Y alloy.

Localized Corrosion Behavior and Corrosion Microstructure of LZ91 and LAZ931 Mg Alloys

LZ91 (Mg-9 wt%Li-1 wt%Zn) and LAZ931 (Mg-9 wt%Li-3 wt%Al-1 wt%Zn) alloys are emerging ultra-lightweight Mg alloys, which can be used in applications that require weight reduction. Although LZ91 alloy has found some success in the 3C industry, the relatively inferior mechanical strength limits its widespread application. To improve the mechanical properties, Al was added to LZ91 alloy to form LAZ931 alloy. However, both LZ91 and LAZ931 alloys are primarily composed of a dual-phase structure with α (HCP) and β (BCC) phases, which form a microgalvanic couple in the corrosion environment. Furthermore, adding Al introduces additional secondary phases, such as AlLi and MgLi2Al, which complicate the corrosion behavior and mechanism. Therefore, this study investigates the corrosion behavior and microstructure of LZ91 and LAZ931 Mg alloys in 3.5 wt% NaCl solution and the relationships to the phase distribution in the alloy substrates.By in situ optical microscope (OM) observations and open circuit potential (OCP) monitoring, localized corrosion initiates on the LAZ931 alloy earlier than on the LZ91 alloy. The early initiation and propagation of localized corrosion on the LAZ931 alloy result in worse corrosion resistances and faster corrosion rates measured by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. By scanning Kelvin probe force microscopy (SKPFM), the Li-rich β phase is more active than the Mg-rich α phase. However, interestingly, localized corrosion was found to preferentially propagate inside the α phase, which seems to contradict the SKPFM measurements. The preferential propagation of localized corrosion in the α phase could be related to the difference in the surface corrosion film thicknesses on the α and β phases before localized corrosion propagation. The localized corrosion behavior and corrosion microstructure of the alloys will be discussed based on electrochemical measurements and site-specific microstructure characterizations. Figure 1

Comparing the Corrosion Behavior and Microstructure of a WE43 Mg Alloy in Simulated Body Fluids Under Different CO2 Conditions

With the low density and high specific strength, magnesium (Mg) alloys are lightweight alloys with various applications. In addition, combined with biocompatibility, similar mechanical properties to human bones, and unique biodegradability, Mg alloys are promising biodegradable implant materials for orthopedic surgeries. However, the degradation rates of Mg alloys are too fast in physiological environments, which limits the clinical applications of Mg implants. Therefore, understanding the corrosion behavior in physiological environments is crucial for developing biodegradable Mg alloys.During Mg alloy degradation, hydroxide (OH-) ions are generated, and the pH near the alloy surface increases. Since carbonate-bicarbonate (CO3 2--HCO3 -) is a vital pH buffer system in the human body, the corrosion behavior of Mg alloys would be affected by the CO2 concentrations of the test environments. In this study, we performed electrochemical and corrosion tests of a solution heat-treated WE43 (Mg-4 wt%Y-3 wt%Nd) alloy in Hanks’ balanced salt solutions (HBSS) at 37°C. By performing the tests in air and in an incubator maintained at 5% CO2, the effect of carbonate-bicarbonate pH buffering on the corrosion behavior and corrosion microstructure of the WE43 Mg alloy was investigated.When testing the WE43 Mg alloy in air, a general corrosion morphology was observed during the 24-hour immersion. In contrast, WE43 Mg alloy tested in the incubator shows a more active surface potential and localized corrosion initiates on the alloy surface in the early stages of immersion. Electrochemical impedance spectroscopy (EIS) analysis shows that WE43 Mg alloy tested in air has better corrosion resistance than in the incubator. Furthermore, the corrosion resistance of the alloy tested in air increases with immersion time but decreases when tested in the incubator. Potentiodynamic polarization curves after 24-hour immersion confirm that the corrosion current density (i corr) of the WE43 Mg alloy tested in the incubator is higher than that when tested in air. The difference in corrosion behavior is owing to the carbonate-bicarbonate pH buffering effect and will be discussed based on corrosion microstructure characterizations. Figure 1

Microstructure, mechanical properties and wear behavior of Mg matrix composites reinforced with Ti and nano SiC particles

This study examines the mechanical properties and wear mechanisms of magnesium (Mg) metal matrix composites reinforced with titanium (Ti) and silicon carbide (SiC) particles. Three different composite formulations were investigated: Mg-30 wt% Ti (A), Mg-25 wt% Ti-5 wt.% SiC (NB), Mg-20 wt% Ti-10 wt% SiC (NC), and Mg-15 wt% Ti-15 wt% SiC (ND). These composites were fabricated through ball milling and spark plasma sintering (SPS). The incorporation of SiC particles significantly enhanced grain refinement and phase formation within the composites. Density analysis revealed that the actual densities of the composites were lower than the theoretical values, with Composite A exhibiting the highest actual density of 2.15 g/cm³ and the lowest porosity of 16.31%. The introduction of SiC particles increased porosity, with Composite NB displaying the highest porosity at 30.58%. Hardness testing indicated that Composite NC, containing 10 wt% SiC, achieved the highest hardness of 137 HV. In contrast, Composite ND, with 15 wt% SiC, showed a reduced hardness of 115 HV, attributed to increased porosity and potential SiC particle agglomeration. Wear behavior was evaluated using a pin-on-disc tribometer. Weight loss measurements indicated that Composite A had the lowest weight loss (1.1–2.1 mg), while Composite NB experienced the highest weight loss (2.8–8.3 mg) due to increased porosity. Composite NC demonstrated a balance with moderate weight loss (2.0–3.8 mg). The coefficient of friction (COF) varied with SiC content and applied loads (2, 4, and 8 N), with Composite A demonstrating the lowest COF values (2.3–2.8) and stable performance across different loads. Composite NB exhibited higher COF values (3.5–4) and significant fluctuations due to elevated porosity and the presence of SiC particles. Composite NC showed better wear resistance and more stable COF values (2.5–2.9) compared to NB and ND.

Enhancing the mechanical properties and osteogenic differentiation of Mg-1 wt.%Ho alloy by tailoring microstructures through extrusion temperatures

This investigation was conducted to explore the impact of extrusion temperature on the microstructure, mechanical properties, and osteogenic differentiation of the as-extruded Mg-1Ho alloy. The Mg-1Ho alloy was extruded at three different temperatures, i.e., 320, 350, and 380 °C, leading to variation in its grain size and texture intensity. With decreasing extrusion temperature, a significant increase was achieved in its room-temperature ultimate tensile strength (UTS) and yield strength (YS). After being subjected to an extrusion temperature of 320 °C, furthermore, Mg-1Ho alloy can effectively promote osteogenic proliferation and differentiation, anti-inflammatory, along with osteogenic gene expression. Our findings emphasized that adding extract from Mg-1Ho alloy extruded at 320 °C enhanced the ability of osteogenesis, demonstrating its potential as a biomaterial to improve cell performance and fate.

Effect of indium and yttrium on the corrosion behavior of AZ63 magnesium alloy

Indium (In) and yttrium (Y) can activate and alleviate the corrosion of magnesium alloy, respectively. The effects of 1 wt% In and 1 wt% Y on the microstructure and electrochemical behaviors of Mg-6 wt%Al-3 wt%Zn (AZ63) magnesium alloy are investigated via materials characterizations associated with electrochemical techniques. The results showed that co-alloying of In and Y would increase the number of intermetallic phases in AZ63 by generating discrete Al2Y phase and continuous Mg17Al12 phase. During the process of corrosion, the corrosion of Mg-6 wt%Al-3 wt%Zn-1 wt%In-1 wt%Y(AZ63InY) initiates from the intermetallic phases and propagates locally. The corrosion products are apt to adhere on the corroded surface, underneath which a severe corrosion takes place due to the enhanced dissolution-reprecipitation effect of In on activating Mg.

Investigation of grain refinement and mechanical properties of nano-TiCN particles reinforced Mg[sbnd]9Al alloy via experiments and sharp-interface model

Addition of nanoparticles (NPs) in the casting process can greatly refine the grain structure of Mg-9 wt% Al alloy. In this work, different volumes of NPs were used to investigate their effect on grain refinement and mechanical properties. Experimental characterizations showed that a mixing zone of NPs-α-Mg at dendrite tip is formed, and the NPs mainly locate in the mixing zone and the intergranular region, but rarely in the intragranular area. The results also showed that the NPs localize to the intragranular region possibly by attaching to large-sized oxides. With the addition of a suitable amount of nano-TiCN particles to the Mg9Al alloy, grain microstructure was refined and mechanical properties improved. In addition, the sharp-interface model (SIM) was used to clarify the possible grain refinement mechanisms. SIM simulations showed that the heterogeneous nucleation induced by NPs may not be a dominant grain refinement mechanism at both slow and high cooling rates. The numerically estimated equivalent solute diffusion coefficients significantly decreased with the increase in NP amount, indicating that NP-induced inhibition of solute diffusion, grain growth restriction, and enhancement of multi-wave nucleation together constitute the dominant grain refinement mechanisms. The present research offers meaningful insights for controlling microstructure formation in the nano-TiCN reinforced Mg9Al alloys.

Corrosion behavior and microstructure of the surface corrosion film of biodegradable WE43 and ZX21 Mg alloys in Hanks’ balanced salt solution

In this study, the corrosion behavior and microstructure of the surface corrosion film of WE43 (Mg-4 wt%Y-3 wt%RE) and ZX21 (Mg-2 wt%Zn-1 wt%Ca) Mg alloys immersed in Hanks’ balanced salt solution (HBSS) at 37 °C are investigated. Through cross-sectional transmission electron microscopy (TEM) analysis, the surface corrosion films formed on both alloys after immersion in HBSS for 24 h are mainly a mixture of magnesium hydroxide (Mg(OH)2) and dicalcium phosphate dihydrate (DCPD) (CaHPO4·2H2O). Nevertheless, the surface corrosion film on WE43 alloy is only 114 ± 17 nm with Ca and P enriched in the outer portion of the film, while the surface corrosion film on ZX21 alloy is thicker (406 ± 50 nm) with some scattered hollow corrosion products on top of the film. The difference in the surface corrosion film thickness and microstructure is because of the faster corrosion rate of the ZX21 alloy, which resulted from the occurrence of localized corrosion on the alloy surface.

Comparison of microstructure, mechanical property, and degradation rate of Mg-1Li-1Ca and Mg-4Li-1Ca alloys.

Mg-1 wt.% Li-1 wt.% Ca (LX11) and Mg-4 wt.% Li-1 wt.% Ca (LX41) alloys share the same hexagonal closed-packed crystalline structure. However, the differences in microstructure, mechanical properties, and degradation rates between the two alloys are not well understood. Hereby, the above three aspects of LX11 and LX41 alloys were studied via optical microscopy, tensile tests, and electrochemical polarization and electrochemical impedance spectroscopy, together with hydrogen evolution. The concentration of the released Mg2+, Ca2+, and Li+ ions was analyzed using a flame atomic absorption spectrophotometer. Results demonstrated that the LX11 alloy was composed of finer α-Mg grains, fewer twins, and smaller volume fractions of the intermetallic phases Mg2Ca than the LX41 alloy. The increasing Li concentration generated a weak decrease in the yield strength of the Mg-Li-Ca alloys, a remarkable increase in elongation to failure, and a stable ultimate tensile strength. The LX11 alloy had better corrosion resistance than the LX41 alloy. The release rate of the cations (Mg2+, Ca2+, and Li+) varied significantly with time. The release rate of metallic ions in Hank's solution cannot reflect the true corrosion rate of Mg-Li-Ca alloys due to the formation of the precipitated corrosion products and their difference in solubility. The dealloying corrosion mechanism of the Mg2Ca phase in Mg-Li-Ca alloys was proposed.

Solute drag-controlled grain growth in magnesium investigated by quasi in-situ orientation mapping and level-set simulations

Critical properties of metallic materials, such as the yield stress, corrosion resistance and ductility depend on the microstructure and its grain size and size distribution. Solute atoms that favorably segregate to grain boundaries produce a pinning atmosphere that exerts a drag pressure on the boundary motion, which strongly affects the grain growth behavior during annealing. In the current work, the characteristics of grain growth in an annealed Mg-1 wt.%Mn-1 wt.%Nd magnesium alloy were investigated by advanced experimental and modeling techniques. Systematic quasi in-situ orientation mappings with a scanning electron microscope were performed to track the evolution of local and global microstructural characteristics as a function of annealing time. Solute segregation at targeted grain boundaries was measured using three-dimensional atom probe tomography. Level-set computer simulations were carried with different setups of driving forces to explore their contribution to the microstructure development with and without solute drag. The results showed that the favorable growth advantage for some grains leading to a transient stage of abnormal grain growth is controlled by several drivers with varying importance at different stages of annealing. For longer annealing times, residual dislocation density gradients between large and smaller grains are no longer important, which leads to microstructure stability due to predominant solute drag. Local fluctuations in residual dislocation energy and solute concentration near grain boundaries cause different boundary segments to migrate at different rates, which affects the average growth rate of large grains and their evolved shape.

Effects of ZnO addition on the microstructure/corrosion, wear and mechanical properties of sintered Mg-Al matrix composites

Magnesium (Mg)-based composites offer outstanding properties, which make them suitable materials for various applications in medical, aerospace and energy sectors, among others. The wide applications of Mg-based composites have attracted continuous effort to increase their properties and performances. Therefore, the present work focused on synthesizing magnesium-aluminium-zinc oxide (Mg-Al-ZnO) composites. Mg-3Al-xZnO (x = 3, 6 and 9 wt%) composites were prepared using powder metallurgy (PM) route. The composite powders and sintered composites were analyzed to determine their microstructures, using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. In addition, the sintering process took place in argon atmosphere at 450 °C. The quantitative analyses of density, porosity, hardness, compressive strength (CS) and corrosion rate (CR) of the composites were performed. Wear performance was also studied with various wear control parameters, such as the sliding velocity (V), sliding distance (D), applied load (P) as well as ZnO content. Pin-on-disc apparatus was used to determine the wear rate (WR) and coefficient of friction (COF) of the innovatively prepared Mg-3 wt%Al-ZnO composites. The experimental study was conducted in accordance with Taguchi's L16 orthogonal design. Signal-to-noise (S/N) ratio analysis was employed to determine the best combination of parameters for WR and COF. Summarily, SEM images confirmed that ZnO particles were uniformly distributed in the composite samples. Statistical technique, called analysis of variance (ANOVA), was adopted to find the significant factor which affected WR and COF. The P significantly affected the WR, followed by the inclusion of ZnO. But, with respect to COF, ZnO reinforcement inclusion affected COF significantly when compared with the P. Both V and D did not affect WR and COF. Hence, the application of the various composite samples should depend on their various responses to friction and wear, especially in working conditions where both quantities are inevitable.

Effect of the microstructure parameters on the corrosion characteristics of Mg-Zn-Ca alloy with columnar structure

Magnesium alloys with homogeneous degradation and controlled degradation rate are desirable for biodegradable materials. In the present work, Mg-3 wt.%Zn-0.2 wt.%Ca alloys with different columnar structures were fabricated and the degradation in 0.9 wt.% NaCl were investigated. With the increase of the growth rate for the directional solidification, the microstructure of the directionally solidified (DSed) alloy evolved from cellular to dendritic coupled with the change of the spacing of the primary trunks (λ1) and the volume fraction (fv) of Ca2Mg6Zn3 phase. The results of the corrosion test suggested that the alloy with cellular structure experienced homogeneous corrosion and exhibited the lowest corrosion rate. The good corrosion resistance of the alloy with cellular structure was attributed to the protective corrosion products film (CPF), which was closely related to the fv of Ca2Mg6Zn3 phase and λ1. To evaluate the corrosion rates (CR) of the DSed Mg-Zn-Ca alloys with different microstructures, a parameter α was proposed in this work, which was calculated by λ1 and the fv of Ca2Mg6Zn3 phase. The fitting result showed that there was a linear relationship between CR and α, which was CR = 4.1899 + 0.00432α. This means that the CR of the DSed Mg-Zn-Ca alloy can be evaluated if the microstructure had been characterized.

Utilizing a unified conceptual dynamic model for prediction of particle size of duel-matrix nanocomposites during mechanical alloying

This work focused on developing an analytical fast and reliable model to predict the morphological changes in nanocomposite powders during mechanical alloying. A conceptual dynamic model was developed and applied to predict the particle size of magnesium-based hybrid composite powder reinforced with Ti and SiC fabricated by mechanical alloying. The effect of milling time on the morphology, microstructure, and particle size of composite powders was investigated. The experimental and model predictions demonstrated that the optimal milling times varies between pure metal, duel matrix alloy and duel-matrix nanocomposite because it was obtained as 32 h for Mg milled, 16 h for Mg-30 wt% Ti and Mg- 20 wt% Ti- 10 wt% SiC nanocomposite with an average particle size 4.91 μm, 6.95 μm, and 5.38 μm, respectively. Prediction results by the CD model for the mentioned samples were equal to 5.33 μm, 6.7 μm, and 6.04 μm, respectively. By increasing the time of ball milling, the crystalline structure of SiC from changed hexagonal to cubic. Another effect of increasing time occurred on the crystallite size and caused the largest decrease, which was equal to 61.91%, to occur for composite Mg-Ti-SiC.

Biotribological behaviour, biodegradability and osteocompatibility of Mg-3Zn/HA composite based intramedullary inserts in avian model

Bioactivity, structural integrity and tribological behaviour of biodegradable orthopaedic fracture fixing accessories considerably impact their actual performance in the body environment. Immune system in the living body quickly responds to the wear debris as foreign material and begins a complex inflammatory response. Magnesium (Mg) based biodegradable implants are widely studied for temporary orthopaedic applications, due to their similar elastic modulus and density to natural bones. However, Mg is highly vulnerable to corrosion and tribological damage in actual service conditions. To address these challenges via a combined approach, the Mg-3 wt% Zinc (Zn)/x hydroxyapatite (HA, x = 0, 5 and 15 wt%) based composites (fabricated via spark plasma sintering route) are evaluated in terms of biotribocorrosion and in-vivo biodegradation and osteocompatibility behaviour in an avian model. The addition of 15 wt% HA in the Mg-3Zn matrix has significantly enhanced the wear and corrosion resistance in the physiological environment. X-ray radiograph analysis of the Mg-HA-based intramedullary inserts implanted in the humerus bone of birds showed consistent progression of degradation and positive tissue response up to 18 weeks. The 15 wt% HA reinforced composites have shown better bone regeneration properties than other inserts. This study provides new insights into developing next-generation Mg-HA-based biodegradable composites for temporary orthopaedic implants, with excellent biotribocorrosion behaviour.

Electron irradiation enhanced precipitation in a Mg-6 wt% Sn alloy in TEM

The precipitation in a Mg-6 wt% Sn alloy under electron irradiation has been investigated by in-situ heat treatment at 200 °C in a transmission electron microscope. Electron irradiation produced a high number density (9.78 ± 1.27 × 1021 m−3) of fine β-Mg2Sn precipitates with the average length close to 15 nm whereas the β-Mg2Sn precipitates formed in the region without electron irradiation have a low number density of 2.55 ± 0.68 × 1019 m−3 and a coarse size averaging around 200 nm. The β-Mg2Sn precipitates formed with and without electron irradiation have the same orientation relationship with the Mg matrix:11¯00Mg//112β,0002Mg//22¯0β with the habit planes parallel to the basal (0001)Mg plane. Experimental results clearly demonstrate that electron irradiation is effective in refining the precipitate distribution in the Mg-6 wt% Sn alloy and the possible underlying mechanisms are discussed in relation to the supersaturation of vacancies and interstitials produced by electron irradiation.

The growth direction selection of inclined dendrites induced by solute interaction: A phase-field study

Columnar dendritic patterns are the predominant microstructures of directional solidified alloys, which control the micro-segregation and largely affect the mechanical properties of the material. Herein, the growth direction selection of inclined columnar dendrites during the directional solidification of a Mg-4 wt.% Li alloy with the hexagonal close-packed (HCP) crystal structure was investigated by means of phase-field simulations. It is found that the DGP law, which suggests the variation of dendrite growth direction with Péclet number Pe (directly related to the pulling velocity and the primary dendrite spacing), is also applicable to HCP-structured materials. However, results at high pulling velocity show a deviation from the DGP law. To characterize the solute distribution variation around the dendrite tip with changing Pe , we defined a quantitative characteristic of solute concentration field. This quantitative characterization proves that the DGP law is dominated by the solute interaction coming from the solute diffusion layers overlap of neighboring dendrites. That is, increasing the primary spacing or the pulling velocity can weaken the solute interaction and result in the rotation of dendrite growth direction to the preferred crystalline direction. The solute interaction does not work when the solute diffusion layer becomes thin enough under very high pulling velocities. The weakening and failure of solute interaction between neighboring dendrites result in the deviation of dendrite growth direction from the DGP law found in this study and previous study. • The growth direction selection of inclined columnar dendrites during the directional solidification of a Mg-4 wt.% Li alloy was investigated through phase-field simulations. • The applicability of DGP law, which suggests the variation of dendrite growth direction with Péclet number Pe , was extended to the HCP-structured materials. • The dominant factor amd limitation of DGP law were clarified by analyzing effects of solute interaction on the growth direction selection of inclined dendrites.

Anomalous In Vitro Corrosion Behaviour of Rolled Mg-1 wt. % Zn Alloy Due to Buffer-Microstructure Interactions

In this study, the influence of microstructure and buffer system on the corrosion behaviour of Mg-1 wt. % Zn is examined. The grain size of the alloy was refined from 700 µm to under 15 µm by rolling with varying reduction percentages per pass. The effects of the rolling procedure on the resulting corrosion profile were analysed with immersion and electrochemical methods. Though the rolling procedure resulted in significant grain refinement, the as-cast samples had the lowest corrosion rate of 2.8 mm/yr, while those of the rolled samples were as high as 15.8 mm/yr. The HEPES buffer system did not control the pH or support the formation of insoluble precipitates as well as the NaHCO3/CO2 buffer system, leading to more severe localised pitting corrosion in samples immersed in HEPES buffered media. While reducing grain size generally corresponds to a lower corrosion rate in Mg alloys, this study provides evidence that other factors such as texture and buffer system must also be considered to accurately test candidate alloys for biodegradable orthopaedic applications.

Microstructural evolution and its effects on the mechanical properties of fine-grained Mg-3Gd during tension

Recrystallized Mg-3 wt. % Gd with an average grain size of 4 μm was prepared and tensioned under different strains (2%, 5%, 10%, and 20%) to investigate the evolution of the deformation mechanism and its effects on the mechanical properties of fine-grained Mg alloy during plastic deformation. The microstructure of the alloy has been characterized using electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The results show that the dislocation density was ∼0.67 × 1014 m−2 at 2% strain, which was accompanied by a few tension twins and <c + a> dislocations. Upon increasing the strain to 5%, the dislocation density was significantly increased to 1.77 × 1014 m−2, which contributes approximately 60% of the flow stress increment when compared to that observed at 2% strain. Meanwhile, tension twins were more frequently observed, while <c + a> dislocations were detected in most of the grains. The dislocation density was slightly increased to 2.31 × 1014 m−2 in the 10% tensile-deformed Mg-3Gd sample, while other strengthening sources became increasingly important. The proportion of low angle grain boundaries (LABs) was almost tripled and compression or double twins are observed. The dislocation density became saturated at ∼2.00 × 1014 m−2 and the proportion of LABs remained unchanged upon further increasing the strain to 20%, although compression or double twins were more frequently detected, which resulted in a low work hardening rate.

Hydrolysis H2 generation behavior of AM50 alloy waste coactivated by Mg-based master alloys

Mg-25 wt%Ni (Mg25Ni) or Mg-30 wt%Ce (Mg30Ce) master alloys were firstly introduced by high-energy ball milling (HEBM) to surface activate AM50 alloy waste and activated AM50-Mg25Ni, AM50-Mg30Ce and AM50-Mg25Ni–Mg30Ce are obtained. The hydrolysis H2 generation behavior are comparatively investigated. The results show that AM50-Mg25Ni with 10 wt% Mg25Ni can rapidly generate 500.1 mL/g H2 within 5 min at 298 K, which is higher than that of AM50 alloy waste (213.9 mL/g H2). Mg30Ce master alloy is unsuitable for activation of AM50 alloy waste due to the deterioration initial hydrolysis kinetics (only 90.3 mL/g H2 in 5 min) originated from the severe agglomeration of AM50-Mg30Ce particles. As high as 427.2 mL/g and 776.5 mL/g H2 can be generated by coactivated AM50-Mg25Ni–Mg30Ce within initial 5 and 30 min, which are higher than those of AM50 alloy waste (213.9 and 715.7 mL/g H2) at 298 K. The thermodynamic behaviors of AM50 alloy waste is accelerated by Mg25Ni and Mg30Ce. The Ea of coactivated AM50-Mg25Ni–Mg30Ce sample is 37.1 kJ/mol, which is lower than that of AM50 alloy waste (52.0 kJ/mol) The coactivation effect and mechanism of Mg25Ni and Mg30Ce is investigated. This work provides an effective activation strategy for modification of Mg alloy waste to generate H2.

Directional-dependent precipitate microstructure and mechanical properties of tensile and compressive stress-assisted aged Mg-Zn alloys

Aging aided by external elastic stress is of scientific interest and practical importance in improving the precipitation hardening response of magnesium alloys. In this work, fiber textured Mg-6 wt.% Zn alloys were subjected to tensile and compressive stress-assisted aging (TSA and CSA, respectively), in which stress is applied along the extrusion direction. Results reveal that the precipitate microstructure, including shape, size, distribution and even internal defect structures exhibits a stress directional dependence. Aberration-corrected scanning transmission electron microscopy shows that a high number density of Zn solute clusters is produced upon CSA, and relatively fine β1’ precipitates are predominantly formed under TSA. First-principles calculations indicate that the stress direction-dependent solute diffusion ability is the leading cause of such directional-dependent precipitate characteristics. Furthermore, TSA generates a higher yield strength than that of stress-free aging (SFA), owing to the relatively high density of fine β1’ precipitates. Compared with SFA and TSA alloys, the CSA alloy contains massive Zn solute clusters and has higher yield strength and better ductility due to the strong cluster-dislocation interactions without the generation of local high stress concentration at the coherent interface. This work offers further insights into altering the precipitation behavior of Mg alloys by applying external stress field and provides possible solutions to achieve high strength-ductility synergy in Mg alloys.