Achieving high catalytic performance with the lowest possible amount of platinum is critical for fuel cell cost reduction. Here we describe a method of preparing highly active yet stable ...electrocatalysts containing ultralow-loading platinum content by using cobalt or bimetallic cobalt and zinc zeolitic imidazolate frameworks as precursors. Synergistic catalysis between strained platinum-cobalt core-shell nanoparticles over a platinum-group metal (PGM)-free catalytic substrate led to excellent fuel cell performance under 1 atmosphere of O
or air at both high-voltage and high-current domains. Two catalysts achieved oxygen reduction reaction (ORR) mass activities of 1.08 amperes per milligram of platinum (A mg
) and 1.77 A mg
and retained 64% and 15% of initial values after 30,000 voltage cycles in a fuel cell. Computational modeling reveals that the interaction between platinum-cobalt nanoparticles and PGM-free sites improves ORR activity and durability.
During the past decades, with the increasing demands in lightweight structural materials, Mg alloys with low density and high performance have been extensively investigated and partly applied in some ...industries. Especially when rare earth (RE) elements are added as major alloying elements to Mg alloys, the alloy strength and creep resistance are greatly improved, which have promoted several series of Mg-RE alloys. This paper reviews the progress and developments of high-performance Mg-RE alloys in recent years with emphasis on cast alloys. The main contents include the alloy design, melt purification, grain refinement, castability, novel liquid casting and semisolid forming approaches, and the industrial applications or trials made of Mg-RE alloys. The review will provide insights for future developments of new alloys, techniques and applications of Mg alloys.
In the application of WE43, it is found that Y2O3 inclusion formed in the process of casting seriously reduced the mechanical properties of the products. The reduction of the mechanical properties is ...even more distinct when it comes to the application in the thin walled complex-precision castings. In order to decrease the Y2O3 inclusions, Gd element was used to replace part of the Y element in Mg-Y-RE series alloys. The effect of Y content (Mg-xY-1Gd-2Nd-0.5Zn-0.5Zr) and Y/Gd ratio (Mg-xY-(5-x)Gd-2Nd-0.5Zn-0.5Zr) on the microstructure and mechanical properties of Mg–Y–RE alloys were investigated in this paper. With decreasing Y content, the grain size of the alloys increased, both ultimate tensile strength (UTS) and yield strength (YS) of alloys decreased monotonically. Replacing part of Y content with Gd and keeping the total rare earth content unchanged, the low Y content Mg-2Y-3Gd-2Nd-0.5Zn-0.5Zr alloy showed the same mechanical properties as the high Y content Mg-4Y-1Gd-2Nd-0.5Zn-0.5Zr alloy at both room and elevated temperatures. After solution treatment at 525 °C for 8 h and aging treatment at 225 °C for 10 h, the UTS, YS and elongation (ε) of Mg-2Y-3Gd-2Nd-0.5Zn-0.5Zr alloy reached 281.7 MPa, 198 MPa and 11.1% at room temperature, and 216.7 MPa, 171.6 MPa and 16.1% at 250 °C. The new low Y content Mg-2Y-2Nd-3Gd-0.5Zn-0.5Zr alloy is expected to replace the high Y content WE43 alloys, which can be used in the complex thin-walled parts of aviation products.
Abstract
Magnesium alloys with high strength and excellent corrosion resistance are always sought-after in light-weighting structural components for automotive and aerospace applications. However, ...for most magnesium alloys that have a high specific strength, they usually have an inferior corrosion resistance and vice versa. In this work, we successfully develop a Mg-11Y-1Al (wt. %) alloy through conventional casting, solution treatment followed by extrusion. The overall properties of this alloy feature with a corrosion rate lower than 0.2 mm y
−1
, high yield strength of 350 MPa and moderate tensile elongation of 8%, the combination of which shows competitive advantage over other comparative magnesium alloys in the literature. It is found that a thin and dense protective film of Y
2
O
3
/Y(OH)
3
can be fast developed with the aid of Al
2
O
3
/Al(OH)
3
deposition to isolate this alloy from further attack of corrosion medium. Meanwhile, the refined grains, weak texture and activation of non-basal slip systems co-contribute to the high strength and good ductility. Our findings are expected to inspire the design of next-generation high performance magnesium alloys.
Zingiber officinale Roscoe extract, Raphanus sativus L. extract, Rheum palmatum extract, Coptis chinensis extract, Glycyrrhiza uralensis extract (GUE), Potentilla discolor extract (PDE) and Taraxacum ...officinale extract (TOE) were screened for the green corrosion inhibitors of AZ91 alloy in saline environment. The experiment results demonstrated that GUE, PDE and TOE can significantly enhance the corrosion resistance of AZ91 alloy by 73.4, 87.6 and 84.6%, respectively. Surface characterization using FTIR, UV-Vis and XPS revealed that the organic compounds of GUE, PDE and TOE can interact with the alloy surface to form a protective physisorbed film, effectively mitigating the corrosion process of AZ91 alloy. The present results may be helpful to discover the new green inhibitors with high inhibition efficiency for AZ91 alloy.
•CEC method was firstly applied on Mg–Zn–Gd alloy and enhanced its mechanical properties greatly.•The growing up of nanoscale I-phase during deformation was firstly observed.•The texture weakening ...effect of I-phase was proved to exist and contributed to the ductility.
Mg–1.5Zn–0.25Gd (at.%) alloy reinforced by icosahedral quasicrystalline phase (I-phase) was fabricated and subjected to cyclic extrusion and compression (CEC) at 350°C to investigate the microstructure evolution during CEC and its effect on the mechanical properties. It is observed that, during CEC, the microstructure of the alloy was greatly refined by dynamic recrystallization (DRX), large numbers of I-phase particles precipitated and then grew up, the texture of the alloy was obviously weakened. These changes in microstructure improved the mechanical properties of the alloy significantly and the alloy processed by 8 passes CEC exhibited outstanding plasticity of 31.4% and moderate yield strength of 161MPa.
This paper investigates the intergranular deformation behavior and its effect on the overall ductility of a Mg-Gd-Y alloy, using in-situ tension in scanning electron microscopy (SEM) combined with ...electron backscattered diffraction (EBSD) and digital image correlation (DIC) techniques. At regions surrounding grain boundaries, the majority of activated dislocation slip traces were found to form in pairs across grain boundary, and the basal-to-basal (B-B) slip pair is the dominant type. Strain accommodation around the grain boundary interfaces is affected by both Schmid factor in the adjacent grains and the m’ value between these main slip systems. A mk value was proposed in this paper as the maximum value of the product of the Schmid factor and the m’ value of the adjacent grains to measure strain accommodation around the grain boundary interface, where a higher mk value would mean a larger local strain. It is suggested that the overall ductility of a Mg alloy could be evaluated by measuring its average mk value. As an evidence, the Mg-Gd-Y alloy tubes with higher mk value generally show higher elongations during tensile tests in this study.
•Most of slip traces were formed in pairs across grain boundary.•Intergranular deformation ability was measured by combining Schmid factor and geometric compatibility factor m’.•Improving strain accommodation around the grain boundary interfaces can improve the ductility of Mg alloys.
The microstructure evolution and mechanical properties of Mg-Gd-Sm-Zr alloys during heat treatment were systematically investigated. The precipitation sequence of an α-Mg supersaturated solid ...solution (S.S.S.S., cph) during aging at 225°C is: S.S.S.S.→β″ (D019)→β′ (cbco)→β1 (fcc)→β (fcc), which is different from previously reported Mg-Gd-Sm systems. The observed shortened incubation periods in the Mg-Gd-Sm-Zr alloys can be mainly attributed to the increased amount of Sm present. Peak-aged Mg-Gd-Sm-Zr alloys exhibit mechanical properties superior to that of the WE54 alloy. The product of strength and elongation (PSE) was used to estimate the toughness of Mg-Gd-Sm-Zr alloys, and the PSE value decreases with increasing RE content.
Nanoscale precipitations in deformed dilute alloying Mg-Zn-RE alloys usually play critical positive roles in mechanical properties, while characterizing them still poses a significant challenge due ...to their small size and low volume fraction. Here, we conduct a systematic structural analysis of the nanoscale secondary phase particles, including W phase, a small amount of I phase and a handful of Mg3Gd phase, in hot deformed dilute alloying Mg-Zn-Gd alloy by combining atomic-resolution transmission electron microscopy with first-principles calculations. The investigation of atomic structure of nanoscale W phase reveals that the stoichiometric composition of W phase is determined by the quantity of Mg atoms which are replaced by Zn at certain positions. Furthermore, nanoscale W phase, I phase and Mg3Gd phase particles could exhibit certain orientation relationships and coherent or semi-coherent interface with Mg matrix, which contributes to atomic bonding at their interfaces. We also identify a phase transition from Mg3Gd phase to W phase, which is further supported by first-principles calculations showing that Mg3Zn3Gd2 phase is energetically more favorable than Mg3Gd phase. The phase transition between W phase and I phase could also take place during hot deformation and is reversible by absorbing or releasing Zn atoms at the interfacial region.
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•Nanoscale precipitations in high performance Mg-Zn-Gd alloy are systematically studied by atomic-resolution TEM/STEM.•The precise position of Zn and Gd atoms in the unit cell of the nanoscale W phase is determined.•Coherent or semi-coherent interface of nanoscale particles with Mg is identified with certain orientation relationships.•Nanoscale Mg3Gd phase is likely to transform to W phase according to STEM-EDS and first-principles calculation results.
A detailed analysis of the plastic deformation characteristics was performed for an extruded ZK60 magnesium alloy under uniaxial cyclic loading along the extrusion direction. The experiments used for ...the analysis were performed under single-step strain-controlled loading, two-step strain-controlled loading, and stress-controlled loading. An elastic limit with an offset of 10−5 plastic strain is used for the demarcation of elastic and elastic-plastic deformation. An inflection point is used to signify a transition of the dominated deformation mechanism from twinning-detwinning to dislocation slips. The macroscopic stress-strain response of the material is intrinsically related to the microstructures of the material during cyclic loading. The elastic limit range is closely related to the microstructure of the material at the peak stress prior to the loading reversal. If the microstructure at the peak stress displays a strong basal a-texture, yielding is dominantly associated with the activation of basal slips. The elastic limit range to activate basal slips for the ZK60 magnesium alloy under investigation is 100 MPa. If the microstructure at the peak stress contains tension twins, the elastic limit range during subsequent loading reversal reflects the activation stress of detwinning/retwinning process, which can be interpreted as the critical stress to activate the gliding of twin boundaries. The stability of twin boundaries is influenced by twin volume fraction, twin morphology, and cyclic hardening. Dependent on the twin volume fraction and loading history, the elastic limit range varies from 20 MPa to 100 MPa for the material under investigation.
•Detailed analysis of cyclic plastic deformation of ZK60 Mg alloy under uniaxial loading.•Microyielding dependent on microstructure at the peak stress prior to the loading reversal.•Constant elastic limit range of 100 MPa for ZK60 Mg alloy when twin-free.•Yielding dominantly associated with the activation of basal slips for basal a-texture.•Elastic limit dependent on twin volume fraction and loading history.
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