The Mg–Ca alloys with 2wt%, 3wt%, 5wt% Al content were fabricated in this paper. After be extruded at 673K with the ratio of 16:1, the microstructures and mechanical properties of the alloys ...influenced by Ca/Al ratio were investigated.Results showed that the category and amount of precipitated secondary phase were influenced obviously by Ca/Al ratio, which changed from Mg2Ca and (Mg, Al)2Ca to Al2Ca as the Ca/Al ratio decreased from 1 to 0.4. Even though the secondary phase was cracked after the application of hot extrusion, the amount, size and distribution of secondary phase were strongly dependent on Ca/Al ratio. The basal plane texture was found in all the as-extruded alloys, the I(101¯0)/I(101¯1) and I(0002)/I(101¯1) values demonstrated different changing tendencies with the variation of Ca/Al ratio. All the UTS, elongation and strain hardening rate of the as-extruded alloys increased with decreasing Ca/Al ratio, however, the YS exhibited the inverse variation tendency. A significant stagnation point was found in the θ-(σ-σ0.2) curve as the Ca/Al ratio is 1, which becomes unobvious with decreasing Ca/Al ratio. The reasons are given and analyzed.
Ti/Al multilayered composites (LMCs) with 3-layers, 5-layers and 7-layers were prepared by hot‐pressing and hot‐rolling. The effects of the interface on the mechanical properties and stamping ...formability of LMCs were revealed. The results indicate that the TiAl
3
phases at the interface thicken gradually with the increase of layers. As the layers of LMCs increases, both the grain size and the basal texture strength of Ti decrease, and Ti possesses a higher Schmid factors (SF) and more uniform SF distribution, which promotes the overall coordinated deformation of LMCs. The elongation (EL) of LMCs gradually increases at the expense of the strength with the increase of layers. The stress–strain transfer across the interface, the release of residual stress through interfacial microcracks, and the improvement of the interfacial metallurgical bonding strength are all conducive to the coordinated deformation between Ti and Al layers, thus the strength of LMCs decreases and the EL enhances. Both the yield strength ratio (σ
s
/σ
b
) and plastic strain ratio (r) decrease, while the strain-hardening exponent (n) increases with the increase of layers of LMCs, which are beneficial to improve the stamping formability of LMCs. The number of interface increases with the increase of layers, which hinders crack propagation. Moreover, the microcracks are easily induced by the brittle TiAl
3
phase at the interface, and the main cracks deflect obviously and release part energy in the form of secondary microcracks, thus delaying the failure of LMCs and improving their stamping formability.
Graphical Abstract
The Mg-4Zn-0.5Ca alloys extruded at 280°C by different ultra-slow extrusion speed (0.01, 0.05, 0.1 and 0.5mms−1) were investigated in present study. The results show that both the volume fraction and ...average size of DRXed grains increase with the increase of extrusion speed, which is different from that depicted by present Z parameter. To fit the extrusion conditions with low temperature and ultra-slow extrusion speed, a more accurate estimate/measurement of the actual temperature in the expression of the Z parameter is needed in the further study. Even though the amount of precipitates decrease with the increasing extrusion speed, the increasing amount of DRX regions lead to the decreased intensity of basal plane texture. Superior mechanical properties with the yield strength of 324.5MPa, ultimate tensile strength of 371.1MPa and elongation to failure of 7.9% are achieved in present Mg-4Zn-0.5Ca alloy extruded at the speed of 0.01mms−1. As the extrusion speed increased from 0.01 to 0.5mms−1, the strength decreases which is accompanied with the increase of elongation.
High strength Mg-9Al serial alloy processed by slow extrusion Kang, Jin-wen; Sun, Xue-fei; Deng, Kun-kun ...
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
06/2017, Volume:
697
Journal Article
Peer reviewed
The AZ91-0.5Ca alloy was extruded at 250°C with slow extrusion speed (0.03, 0.3, 3mm/s) in the current study. The results showed that both the volume fraction and average grain size of DRXed grains ...increased with the increase of extrusion speed. Furthermore, numerous fine Mg17Al12 phase were observed in the DRXed regions of the extruded alloys, the amount of which decreased by increasing extrusion speed. The decrease of extrusion speed led to the improvement of yield strength and ultimate tensile strength, however, at the expense of elongation. As the extrusion speed decreased to 0.03mm/s, the yield strength, ultimate tensile strength and elongation of present alloy were ~347.8MPa, ~402.2MPa and ~9.1%, respectively, which were superior to the present commercial Mg-Al serial alloys. Detailed reasons are given and analyzed.
The 5μm10 vol % SiCp/AZ91 composite was extruded successfully at 250 °C by the slow speed extrusion (0.01, 0.1 and 1 mm/s). Results indicated that the composite with the yield strength of ∼371.5 MPa ...and ultimate tensile strength of ∼443.9 MPa exhibited much higher tensile strength than present particle reinforced magnesium matrix composites (PMMCs). Such high tensile strength in present work might be attributed to ultra-fine grains and submicron sized Mg17Al12 phases precipitated during extrusion. As the extrusion speed increased from 0.01 to 1 mm/s, both the average size of grains and Mg17Al12 phase increased, while volume fraction of Mg17Al12 phase decreased. All these led to the decrease of yield strength and ultimate tensile strength, however, accompanied by the increase of elongation.
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•Ultra-fine grain is achieved by slow-speed extrusion in SiCp/AZ91 composites.•Large amount of fine Mg17Al12 phases precipitate during extrusion process.•Superior strength (YS of 371.5 MPa, UTS of 443.9 MPa) is obtained in present work.•Ultra-fine grain plays a dominant role in such high strength of PMMCs.
Arranging ionic liquids (ILs) with long‐range order can not only enhance their performance in a desired application, but can also help elucidate the vital between structure and properties. However, ...this is still a challenge and no example has been reported to date. Herein, we report a feasible strategy to achieve a crystalline IL via coordination self‐assembly based reticular chemistry. IL1MOF, was prepared by designing an IL bridging ligand and then connecting them with metal clusters. IL1MOF has a unique structure, where the IL ligands are arranged on a long‐range ordered framework but have a labile ionic center. This structure enables IL1MOF to break through the typical limitation where the solid ILs have lower proton conductivity than their counterpart bulk ILs. IL1MOF shows 2–4 orders of magnitude higher proton conductivity than its counterpart IL monomer across a wide temperature range. Moreover, by confining the IL within ultramicropores (<1 nm), IL1MOF suppresses the liquid–solid phase transition temperatures to lower than −150 °C, allowing it to function with high conductivity in a subzero temperature range.
A reticular chemistry based strategy opens a facile toolbox for designing liquid molecules with long‐rang‐ordered framework of MOF. IL1MOF is the first crystalline ionic liquid (IL) combining a balance of good mechanical properties and high conductivity. It expands the use of IL electrolytes to an low temperature region.
The SiCp/Mg-xAl-2Ca composite with different (2, 3, 5 and 9 wt%) Al content is fabricated by stir casting. After be extruded at 673 K with the ratio of 16:1, the microstructures and mechanical ...properties of the composites are investigated. As compared with Mg-xAl-2Ca alloys, the addition of SiCp has no obvious effect on the category of precipitated phase, but increases its volume fraction and is propitious to the uniformity of microstructures. With the application of extrusion, precipitated phase is refined and its distribution is improved obviously. The yield strength of the composites increases with the increasing of Al content as a result of an increased amount of precipitated phase. The ultimate tensile strength and elongation are improved as the Al content increased from 2 wt% to 5 wt%, but deterioration happens when the Al content is increased to 9 wt%. Addition of SiCp lows down the strength of Mg-2Al-2Ca alloy, however, leads to the increased strength of Mg-3Al-2Ca alloy and Mg-5Al-2Ca alloy. Even though the yield strength of SiCp/Mg-9Al-2Ca composite is similar to Mg-9Al-2Ca alloy, it owns a lower ultimate tensile strength.
In this study we execute a rational screen to identify Chinese medical herbs that are commonly used in treating viral respiratory infections and also contain compounds that might directly inhibit ...2019 novel coronavirus (2019-nCoV), an ongoing novel coronavirus that causes pneumonia.
There were two main steps in the screening process. In the first step we conducted a literature search for natural compounds that had been biologically confirmed as against sever acute respiratory syndrome coronavirus or Middle East respiratory syndrome coronavirus. Resulting compounds were cross-checked for listing in the Traditional Chinese Medicine Systems Pharmacology Database. Compounds meeting both requirements were subjected to absorption, distribution, metabolism and excretion (ADME) evaluation to verify that oral administration would be effective. Next, a docking analysis was used to test whether the compound had the potential for direct 2019-nCoV protein interaction. In the second step we searched Chinese herbal databases to identify plants containing the selected compounds. Plants containing 2 or more of the compounds identified in our screen were then checked against the catalogue for classic herbal usage. Finally, network pharmacology analysis was used to predict the general in vivo effects of each selected herb.
Of the natural compounds screened, 13 that exist in traditional Chinese medicines were also found to have potential anti-2019-nCoV activity. Further, 125 Chinese herbs were found to contain 2 or more of these 13 compounds. Of these 125 herbs, 26 are classically catalogued as treating viral respiratory infections. Network pharmacology analysis predicted that the general in vivo roles of these 26 herbal plants were related to regulating viral infection, immune/inflammation reactions and hypoxia response.
Chinese herbal treatments classically used for treating viral respiratory infection might contain direct anti-2019-nCoV compounds.
The as-cast Mg-4Zn-2Gd-0.5Ca alloy mainly contained I phase and W phase, while the I phase dissolved into Mg substrate after homogenization treatment which improved the alloy’s corrosion resistance. ...After the application of multidirectional forging (MDF), the grains were refined obviously accompanied with the precipitation of I phase. With the increasing pass of MDF, both the size of dynamic recrystallized grains and the amount of precipitated I phase increased. The corrosion resistance of Mg-4Zn-2Gd-0.5Ca alloy became worse after 1 pass of MDF as compared with the as-homogenizated condition because of the precipitation of I phase. Neverthless, the corrosion resistance of the as-MDFed Mg-4Zn-2Gd-0.5Ca alloy deteriorated with the increasing pass of MDF. As compared with grain refinement, the precipitated I phase is thought to play a main role on the corrosion behavior of Mg-4Zn-0.5Ca alloy.
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•Dissolution of I phase lead to the improved corrosion resistance of as-HTed alloy.•MDF results in the grain refinement and precipitated I phase of Mg-4Zn-2Gd-0.5Ca alloy.•The influence of precipitated I phase on corrosion resistance is larger than grain refinement.
The redox mediated photoelectrochemical (PEC) or electrochemical (EC) alkene oxidation process is a promising method to produce high value‐added epoxides. However, due to the competitive reaction of ...water oxidation and overoxidation of the mediator, the utilization of the electricity is far below the ideal value, where the loss of epoxidation's faradaic efficiency (FE) is ≈50%. In this study, a Br−/HOBr‐mediated method is developed to achieve a near‐quantitative selectivity and ≈100% FE of styrene oxide on α‐Fe2O3, in which low concentration of Br− as mediator and locally generated acidic micro‐environment work together to produce the higher active HOBr species. A variety of styrene derivatives are investigated with satisfied epoxidation performance. Based on the analysis of local pH‐dependent epoxidation FE and products distribution, the study further verified that HOBr serves as the true active mediator to generate the bromohydrin intermediate. It is believed that this strategy can greatly overcome the limitation of epoxidation FE to enable future industrial applications.
A method of PEC Br−/HBrO mediated alkene epoxidation with a near‐quantitative selectivity and 100% FE is achieved by modulating Br− concentration and the local acidity around the interface of α‐Fe2O3 photoanode, in which bromohydrin product is identified as the intermediate and transformed to epoxide with the removal of HBr when meeting OH−.
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