Microstructures, tensile properties and high cycle fatigue behavior of sand-cast Mg–Gd–Y–Zr alloys with different Gd and Zr contents have been investigated. With decreasing Gd content from 9 to ...11wt%, the amount of eutectic phase in sand-cast Mg–xGd–3Y–0.5Zr alloys and of the β′ precipitates in peak-aged (T6) conditions decreased, and increasing Zr content from 0.3 to 0.5wt% led to a decrease in the grain size. The variation of Gd content had a slight influence on the tensile properties, while Zr content had an obvious influence on the tensile properties particularly the elongation. Gd and Zr affected the fatigue behavior in different ways, i.e. the increase of Zr content improved the fatigue strength while the increase of Gd content extends the fatigue life under relatively high stress.
In this work, solution and low-temperature (50–125 °C) aging treatment is utilized to develop a novel Mg-Li alloy with an excellent combination of strength and ductility. After optimizing the ...solution time, effects of aging treatment on microstructure and mechanical properties of the Mg-8Li-3Al-2Zn-0.5Y alloy were investigated. The highest strength is obtained after solution heat treatment at 350 °C for 4 h, accompanied with relatively low ductility. The following low-temperature aging treatment is used to balance the strength and ductility. With the increase of aging temperature, the ductility of the alloy was improved, accompanied by continued decrease in strength. The formation and aggregation of Al-Li phase during aging treatment is the major factor that influences the mechanical properties of the aged alloys. The reduced solid solution strengthening of Al and the aggregation of Al-Li phase are detrimental to strength. The evolution of Al-Li phase during aging treatment at different temperature is analyzed in detail. Through promoting the precipitation and preventing the aggregation of Al-Li phase by optimizing aging temperature, well-designed low-temperature aging treatment (75 °C × 4 h) results in favorable microstructural evolution and optimum combination of strength (yield strength = 216 MPa, ultimate tensile strength = 276 MPa) and ductility (elongation = 11.1%).
•The reduced solid solution strengthening of Al and the aggregation of Al-Li phase are detrimental to strength.•The evolution of Al-Li phase during aging treatment at different temperature is analyzed in detail.•Well-designed aging treatment results in optimum combination of strength and ductility.
This study was undertaken to investigate the influence of Er addition on microstructure and mechanical properties of as-cast Mg-10Li-5Zn alloy. With addition of Er, the grain size of as-cast alloys ...is greatly reduced, meanwhile, Mg-Zn-Er phase forms and increases gradually and Mg-Li-Zn phase decreases. The Mg-Zn-Er phase is mainly W-phase. The size of W-phase becomes larger with the increase of Er content from 0.5 wt% till 3.5 wt% and W-phase is mainly distributed from in the grain interiors to along the grain boundaries as well. The size, quantity and distribution of W-phase is an important factor that influences the mechanical properties of Mg-10Li-5Zn-xEr alloys. Overmuch coarse W-phase in the grain boundaries is detrimental to strength. The Mg-10Li-5Zn-0.5Er alloy exhibits an optimum combination of tensile properties with the ultimate tensile strength, yield strength and elongation of 198 MPa, 223 MPa and 14.7%. The optimal Er addition in as-cast Mg-10Li-5Zn alloy is ~0.5 wt%.
Mg based Mg–Rare earth (RE) hydrogen storage nano-composites were prepared through an arc plasma method and their composition, phase components, microstructure and hydrogen sorption properties were ...carefully investigated. It is shown that the Mg–RE composites have special metal-oxide type core–shell structure, that is, ultrafine Mg(RE) particles are covered by nano-sized MgO and RE2O3. In comparison to pure Mg powders prepared using the same method, the hydrogen absorption kinetics can be significantly improved through minor addition of RE to Mg. In addition, the Mg–RE composite powders show better anti-oxidation ability than pure Mg powders, resulting in the increased hydrogen storage capacity of Mg–RE powders over pure Mg powders. In particular, the hydrogenation enthalpy can be increased and the dehydriding temperature can be reduced through minor addition of Er. The experimental results show that both the RE in solid solution state in Mg and the RE2O3 nano-grains covered on Mg particles contribute to the improved hydrogen storage thermodynamic, kinetic and anti-oxidation properties of Mg ultrafine particles.
► RE (RE = Nd, Gd, Er) doped Mg based composites are prepared by arc plasma method. ► Mg–RE powders are composed of Mg(RE) ultrafine particles covered by MgO/RE2O3. ► Both RE in Mg and RE2O3 on Mg particles improve hydrogen sorption properties. ► Mg–RE composite powers show higher anti-oxidation ability than Mg powders.
A reflection upon the recent developments of semisolid rheoforming techniques of magnesium (Mg) alloys is vital for successfully shaping the future landscape of lightweight and high-performance metal ...materials. In our paper, formation mechanisms of non-dendritic structure were firstly reviewed, and slurry preparation methods as well as rheoforming processes of Mg alloys were then summarized. Afterwards, microstructures and mechanical properties of semisolid Mg alloys were elaborated. The various formation mechanisms of non-dendritic structures provide theoretical bases for understanding the microstructure evolution of semisolid metal slurries. Despite the abundant slurry preparation methods to date, inexpensive industrial solutions for producing high-quality Mg alloy slurries are still scarce, which is constituting one of many key challenges in the future. In the case of rheoforming processes, high pressure die casting (HPDC) and squeeze casting are the most promising processes for mass production of semisolid Mg alloys. At present, researches on semisolid Mg alloys are mainly focused on AZ and AM series alloys. To develop high-performance semisolid Mg alloys, the slurry preparation and rheoforming technology of Mg-RE alloys are worthy of further investigation.
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•Formation mechanisms of non-dendritic structures during rheological slurry preparation are elaborated.•Methods of rheological slurry preparation and rheoforming processes of Mg alloys are reviewed.•Microstructure and mechanical properties of semisolid Mg alloys are summarized.•Current challenges and perspectives for future research are discussed.
We report a Mg alloy Mg-2.2Nd-0.1Zn-0.4Zr (wt.%, denoted as JDBM-2) showing great potential in clinical vascular stent application by integrating the advantages of traditional medical stainless steel ...and polymer. This alloy exhibits high yield strength and elongation of 276 ± 6 MPa and 34.3 ± 3.4% respectively. The JDBM-2 with a stable degradation surface results in a highly homogeneous degradation mechanism and long-term structural and mechanical durability. In vitro cytotoxicity test of the Mg extract via human vascular endothelial cells (HUVECs) indicates that the corrosion products are well tolerated by the tested cells and potentially negligible toxic effect on arterial vessel walls. This alloy also exhibits compromised foreign body response (FBR) determined by human peripheral blood derived macrophage adhesion, foreign body giant cell (FBGC) formation and inflammatory cytokine and chemokine secretion. Finally, vascular stents manufactured from the JDBM-2 were implanted into rabbits for long-term evaluation. The results confirm excellent tissue compatibility and up to 6-month structural and mechanical integrity of the stent in vivo. Thus, the JDBM-2 stent with up to 6-month structural and mechanical integrity and excellent tissue compatibility represents a major breakthrough in this field and a promising alternative to traditional medical stainless steel and polymer for the clinical application.
Highlights
A comprehensive discussion of the recent advances in the nanostructure engineering of Mg-based hydrogen storage materials is presented.
The fundamental theories of hydrogen storage in ...nanostructured Mg-based hydrogen storage materials and their practical applications are reviewed.
The challenges and recommendations of current nanostructured hydrogen storage materials are pointed out.
With the depletion of fossil fuels and global warming, there is an urgent demand to seek green, low-cost, and high-efficiency energy resources. Hydrogen has been considered as a potential candidate to replace fossil fuels, due to its high gravimetric energy density (142 MJ kg
−1
), high abundance (H
2
O), and environmental-friendliness. However, due to its low volume density, effective and safe hydrogen storage techniques are now becoming the bottleneck for the "hydrogen economy". Under such a circumstance, Mg-based hydrogen storage materials garnered tremendous interests due to their high hydrogen storage capacity (~ 7.6 wt% for MgH
2
), low cost, and excellent reversibility. However, the high thermodynamic stability (ΔH = − 74.7 kJ mol
−1
H
2
) and sluggish kinetics result in a relatively high desorption temperature (> 300 °C), which severely restricts widespread applications of MgH
2
. Nano-structuring has been proven to be an effective strategy that can simultaneously enhance the ab/de-sorption thermodynamic and kinetic properties of MgH
2
, possibly meeting the demand for rapid hydrogen desorption, economic viability, and effective thermal management in practical applications. Herein, the fundamental theories, recent advances, and practical applications of the nanostructured Mg-based hydrogen storage materials are discussed. The synthetic strategies are classified into four categories: free-standing nano-sized Mg/MgH
2
through electrochemical/vapor-transport/ultrasonic methods, nanostructured Mg-based composites via mechanical milling methods, construction of core-shell nano-structured Mg-based composites by chemical reduction approaches, and multi-dimensional nano-sized Mg-based heterostructure by nanoconfinement strategy. Through applying these strategies, near room temperature ab/de-sorption (< 100 °C) with considerable high capacity (> 6 wt%) has been achieved in nano Mg/MgH
2
systems. Some perspectives on the future research and development of nanostructured hydrogen storage materials are also provided.
Graphical Abstract
Isothermal hot compression at the temperature range of 573–698K and strain rates of 0.005–1.0s−1 was used to investigate the flow behavior and processing characteristics of the nano-SiCp/AZ91 ...composites. Effects of the incorporated particles and their particulate size on the workability of the base alloy were then compared and discussed. Results show that compared with the monolithic AZ91 alloy, the incorporated nano-SiC particles effectively increase the flow stress of the composites by blocking the strain-induced dislocations, while effect of the micro-SiC particles varies due to the competition between pinning effect and particle stimulating nucleation (PSN) mechanism. Three domains of peak energy dissipation efficiency are identified in the processing map and the corresponding microstructures examined by EBSD indicate that continuous dynamic recrystallization (DRX) occurs during the compression. The instability characteristics at low temperature are severe mechanical twinning and micro-cracks, while that at high temperature is intergranular cracking. The incorporation of SiC particles enhances the high temperature (>655K) workability of AZ91 by increasing the upper limit of the processing strain rate and enables low temperature processing by decreasing the lower limit of the temperature. However, the added particles impose a side effect by enlarging the instability domain of the base alloy to a lower strain rate and even higher temperature.
The main challenge for the application of magnesium and its alloy as degradable biomaterials lies in their high degradation rates in physiological environment. In the present work, the biodegradable ...behavior of a patent magnesium alloy Mg–Nd–Zn–Zr (JDBM) and a reference alloy AZ31 was systematically investigated in Hank's physiological solution. The corrosion rate of JDBM (0.28mm/year) was much slower than that of AZ31 (1.02mm/year) in Hank's solution for 240h. After corrosion products were removed, smooth surface of the JDBM was observed by SEM observation compared to many deep pits on the surface of AZ31. Open-circuit potential and potentiodynamic polarization results manifested that pitting corrosion did not occurred on the surface of JDBM at the early period of immersion time due to the formation of a more protective and compact film layer suggested by electrochemical impedance spectroscopy study. The corrosion rate of magnesium alloys was found to slow down in dynamic corrosion in comparison with that in the static corrosion. This provided the basis for scientific evaluation of in vitro and in vivo corrosion behavior for degradable biomagnesium alloy. The present results suggest that the new patent magnesium alloy JDBM is a promising candidate as degradable biomaterials and is worthwhile for further investigation in vivo corrosive environment.
The eutectic morphology of in Al-5Ce alloy was tuned from lamellar to fiber using permanent magnet stirring (PMS) during casting. Superior mechanical properties were achieved in Al-5Ce alloy with ...fiber structure. Lamellar-to-fiber transition is quantitatively modeled within Jackson–Hunt framework. This is the first observation of producing fiber structure of Al-5Ce alloy during permanent mold casting, which sheds light on utilizing PMS to improve mechanical properties of Al-Ce alloys.
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