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In the present work, a novel low-temperature heat-treatable recycled die-cast Al–Mg alloy was developed by adding Zn into non-heat-treatable Al–5Mg–1.5Fe–0.5Mn alloy. The results showed that Zn additions resulted in the formation of equilibrium phase T-Mg32(Al, Zn)49 under as-cast condition, which can be dissolved into the α-Al matrix at a relatively low solution temperature (430 °C) and thus set the base for the low-temperature heat treatment. The mechanical test results indicated that Zn additions had a smooth liner improvement in the strength of all as-cast alloys and T6-state alloys with 1% and 2% Zn as its concentration increased but resulted in a sharp improvement on the strength of T6-state alloy when Zn concentration increased from 2 to 3%. TEM analysis revealed that the precipitate in T6-state Al–5Mg–1.5Fe–0.5Mn–3Zn alloy is η′ phase, rather than the widely reported T″ or T′ phase in other Al–Mg–Zn alloys with approximately same Mg and Zn concentrations. After the optimized low-temperature T6 heat treatment (solution at 430 °C for 60 min and ageing at 120 °C for 16 h), the Al–5Mg–1.5Fe–0.5Mn–3Zn alloy exhibits the yield strength of 321 MPa, ultimate tensile strength of 445 MPa and elongation of 6.2%.

M–Nb–O compounds are regarded as advanced anode materials of lithium-ion batteries owing to their large capacities, high safety and fast Li+ transport. However, challenges remain in the exploitation of new M–Nb–O compounds with low strains to enable superior cyclability. Here, we exploit V3Nb17O50 as a low-strain M–Nb–O anode compound, and V3Nb17O50 micron-sized particles (V3Nb17O50-MP) and submicron-sized rods (V3Nb17O50-SR) are demonstrated. V3Nb17O50 owns an open and robust shear ReO3 crystal structure, which is constructed by 3 ​× ​3 ​× ​∞ (V,Nb)O6 octahedron-blocks linked by VO4 tetrahedra. The resulting A–B–A layered structure with a large interlayer spacing enables the superior Li+ diffusivity and significant intercalation-pseudocapacitive behavior in V3Nb17O50. The maximum unit-cell volume expansion of V3Nb17O50 discharged to 0.8 ​V is only 3.46% (the smallest value among the known M–Nb–O anode compounds with shear ReO3 structures), leading to the excellent cyclability of V3Nb17O50-MP/V3Nb17O50-SR with 90.0/91.8% capacity retention over 2000 cycles at 10C. V3Nb17O50-MP/V3Nb17O50-SR further exhibits a safe operating potential of 1.736/1.724 ​V, large reversible capacity of 207/254 ​mA ​h g−1 at 0.1C, and high rate performance with 68/123 ​mA ​h g−1 at 10C. A LiMn2O4//V3Nb17O50-SR full cell also exhibits comprehensively good electrochemical properties, including excellent cyclability with 85.7% capacity retention over 500 cycles at 5C. Therefore, V3Nb17O50 can be a very promising anode compound for stable, safe, large-capacity and fast-charging Li+ storage.

To meet the demand of high power and energy densities of Li-ion batteries, M-Nb-O compounds are of significance due to not only the intercalation pseudocapacitance but also the high theoretical capacities and excellent cycling stability. However, the exploration of M-Nb-O is very limited. Herein, we firstly report GaNb49O124 as a novel intercalation-type M-Nb-O anode material. GaNb49O124 microspheres (GaNbO-S) with an average diameter of ∼2 μm are fabricated through a hydrothermal method. Benefiting from the nanosized architecture, GaNbO-S delivers superior electrochemical performance in Li-ion batteries. A large reversible specific capacity of 294 mAh g−1 is obtained at 50 mA g−1, while 205 mAh g−1 is reached at 4000 mA g−1. Furthermore, GaNbO-S delivers long-term cycling life with a 72.0% capacity retention over 1800 cycles at 2000 mA g−1. Thus, GaNb49O124 microspheres could be developed as an efficient anode material for Li-ion batteries.

This paper describes the syntheses and electrochemical properties of a new niobate compound, aluminum niobate (AlNb11O29), for Li+ storage. AlNb11O29-microsized particles and nanowires were synthesized based on the solid-state reaction and solvothermal methods, respectively. In situ X-ray diffraction results confirmed the intercalating mechanism of Li+ in AlNb11O29 and revealed its high structural stability against cycling. The AlNb11O29 nanowires with a novel bamboo-like morphology afforded a large interfacial area and short charge transport pathways, thus leading to the observed excellent electrochemical properties, including high reversible Li+-storage capacity (266 mA h g-1), safe operating potential (around 1.68 V), and high initial Coulombic efficiency (93.3%) at 0.1 C. At a very high rate (10 C), the AlNb11O29 nanowires still exhibited a capacity as high as 192 mA h g-1, indicating their good rate capability. In addition, at 10 C, 96.3% capacity was retained over 500 cycles, indicating superior cycling stability. A full cell fabricated with AlNb11O29 nanowires as the anode and LiNi0.5Mn1.5O4 microparticles as the cathode delivered a high energy density of 390 W h kg-1 at 0.1 C. This work suggests that the AlNb11O29 nanowires hold a great promise for the development of high-performance lithium-ion batteries for large-scale energy-storage applications.

Intercalation-type niobium-based oxides are considered as promising anode materials for lithium-ion batteries owing to their high theoretical/practical capacities, long-term cyclability, and high safety. However, studies in this research field are still very limited. Here, we explore MoNb12O33 as the first molybdenum niobium oxide anode material, and prepare microsized MoNb12O33 particles (M-MoNb12O33) and porous MoNb12O33 microspheres (P-MoNb12O33) based on solid-state reaction and solvothermal methods, respectively. MoNb12O33 shows a Wadsley–Roth crystal structure, consisting of 3 × 4 × ∞ NbO6 octahedra linked by corner-sharing MoO4 tetrahedra. This very open and stable structure results in fast Li+ diffusivity and superior structural stability, respectively. These structural merits together with the nanosizing effects in P-MoNb12O33 lead to outstanding electrochemical properties in its half cell, including a high practical capacity (321 mA h g−1 at 0.1C), significant intercalation pseudocapacitive contribution (85.5% at 1.1 mV s−1), prominent rate capability (200 mA h g−1 at 10C), and superior cyclability (capacity retention of 95.7% after 1000 cycles at 10C). Moreover, outstanding electrochemical properties of a LiMn2O4//P-MoNb12O33 full cell are also achieved, such as a high reversible capacity (274 mA h g−1 at 0.1C), good rate capability (106 mA h g−1 at 10C), and superior cyclability (capacity retention of 93.9% after 1000 cycles at 5C). All these findings indicate that P-MoNb12O33 can be a practical anode material for high-capacity, safe, rapid and durable Li+ storage.

A high strength (Yield strength ≥ 320 MPa) and high ductility (Tensile elongation ≥ 10%) die–cast aluminium alloy was first developed. The AlSiCuMgMn alloy processed by high pressure die casting can provide the high yield strength of 321 MPa, the high ultimate tensile strength of 425 MPa and the high ductility of 11.3%, after solution treated at 510 °C for 30 min and aged at 170 °C for 12 h. The alloy demonstrated 150% increase in ductility over the reported most advanced die–cast aluminium alloy, also comparable tensile properties to the 6000 series wrought aluminium alloys but with much lower manufacturing cost. The as–cast microstructure of the alloy mainly contained the primary α 1 –Al phase solidified in the shot sleeve, the secondary α 2 –Al phase solidified in the die, the Al–Si eutectic phase and the intermetallic phases Q–Al 5 Cu 2 Mg 8 Si 6 and θ–Al 2 Cu. The intermetallic phases Q and θ were dissolved into the α–Al matrix during solution. Nanoscale precipitates Q′ and θ′ were precipitated from the α–Al matrix for the strengthening of the alloy through ageing treatment. Multiple effects resulted in the high ductility of the alloy.

W5Nb16O55 is a very promising negative electrode compound for lithium-ion storage owing to its good safety, durable cyclability and high rate performance. However, its commercialization is hindered by its limited capacity and high tungsten cost. Here, we designed a tungsten-free and niobium-rich zinc niobate (Zn2Nb34O87) with a large capacity (theoretically 389 mA h g−1) as a new insertion negative electrode compound. Micron-sized Zn2Nb34O87 blocks (Zn2Nb34O87-B) and one-dimensional Zn2Nb34O87 nanofibers (Zn2Nb34O87-N) were prepared via a solid-state reaction and electrospinning methods, respectively. Zn2Nb34O87-B and Zn2Nb34O87-N have 3 × 4 × ∞ shear ReO3 crystal structures of orthorhombic and monoclinic types, respectively. Both the Zn2Nb34O87 materials exhibited better electrochemical performance than W5Nb16O55 in terms of the capacity, lithium-ion diffusion coefficient, intercalation pseudocapacitive contribution, rate performance, and cyclability. In situ X-ray diffraction characterization demonstrated the excellent structural stability and electrochemical reversibility of Zn2Nb34O87, and revealed that lithium ions were stored in the (010) crystallographic planes. Furthermore, a LiNi0.5Mn1.5O4‖Zn2Nb34O87-N full cell exhibited outstanding electrochemical performance, including a large capacity, prominent rate performance, and especially ultra-long cyclability (96.5% capacity retention even after 1000 cycles at 5C). Therefore, Zn2Nb34O87 holds great promise as a practical negative electrode compound for large-capacity, cost-effective, rapid, durable and safe lithium-ion storage.

Nb16W5O55 is considered as a promising anode material for lithium-ion batteries (LIBs) due to its high safety, good cyclability and high rate performance. However, it has not been practically used since it suffers from its limited capacity. Here, we demonstrate the design and synthesis of a tungsten-free and niobium-rich Al0.5Nb24.5O62 anode material having a very large theoretical capacity of 400 mA h g−1 and a stable shear ReO3 crystal structure. Both Al0.5Nb24.5O62 microsized particles (Al0.5Nb24.5O62-M) and porous microspheres (Al0.5Nb24.5O62-P) were successfully synthesized. In situ X-ray diffraction indicated the intercalated characteristic of Al0.5Nb24.5O62 and revealed the Li+ insertion into/extraction from its (010) crystallographic planes with high structural stability. Consequently, Al0.5Nb24.5O62-P exhibited a large practical capacity (321 mA h g−1 at 0.1C) and good cyclability (90.0% capacity retention after 500 cycles at 10C). In addition, Al0.5Nb24.5O62-P exhibited significant intercalation pseudocapacitive behavior (86.1% pseudocapacitive contribution at 1.1 mV s−1), high rate performance (192 mA h g−1 at 10C), high initial coulombic efficiency (94.9%) and safe working potential (∼1.68 V). Al0.5Nb24.5O62 also performed well in a LiNi0.5Mn1.5O4//Al0.5Nb24.5O62-P full cell. These research results indicate that Al0.5Nb24.5O62 is a practical anode material for high-energy, stable, fast-charging and safe LIBs.

High as-cast strength die-cast AlSi9Cu2Mg alloy was achieved with industrially acceptable ductility, via the addition of titanium diboride nanoparticles. The main intermetallic compounds in the die-cast AlSi9Cu2Mg alloy were identified as θ–Al2Cu and Q–Al5Cu2Mg8Si6 phases. The Fe-rich compound formed in the present die-cast alloy with a high Mn/Fe ratio of 3:1 was determined as the BCC structured α–Al15(Fe,Mn)3Si2 phase with a lattice parameter of a = 1.2702 nm, and the Fe-rich compound had highly faceted morphology with {110} surface termination. The Al matrix phase in the die-cast AlSi9Cu2Mg alloy was refined by ∼65% from 18.1 μm to 6.4 μm, after adding 3.0 wt% titanium diboride nanoparticles. The titanium diboride nanoparticles in the alloy showed coherent interface with the Al matrix, with the (11-1) lattice face of Al parallel to the (0001) lattice face of titanium diboride. The as-cast AlSi9Cu2Mg alloy containing 3.0 wt% titanium diboride nanoparticles exhibited the high yield strength of 233 ± 3 MPa and the tensile strength of 398 ± 7 MPa, as well as the industrially acceptable elongation of 4.8 ± 0.7%, and it showed at least 23% improvement in the as-cast yield strength over the existing die-cast Al alloys. The strengthening by nanoparticle and coherent interface (∼32 MPa) was higher than that by the refining of Al matrix (∼10 MPa). The addition of titanium diboride nanoparticles also affected the fracture of the die-cast AlSi9Cu2Mg alloy, and cracks were prone to form in the Q and Fe-rich compounds, after the addition of titanium diboride nanoparticles.

The effects of varying Mg and Si levels on the microstructural inhomogeneity and eutectic Mg2Si morphology in die-cast Al–Mg–Si alloys have been investigated. It was found both Mg and Si additions decreased the microstructural inhomogeneity by producing more well distribution of primary α-Al and Al–Mg2Si eutectics, but had contrary effects on eutectic Mg2Si morphology. The increasing Mg level transformed eutectic Mg2Si from rod or lamellae to curved flake with larger eutectic spacing λ, while the increasing Si level promoted the formation of rod-like or lamellar eutectic Mg2Si with smaller λ. The reason for the above evolutions can be traced back to alloys’ solidification behaviour. Thermodynamic calculation indicates that both Mg and Si decrease the liquidus temperature and suppress the precipitation of coarse primary α-Al grains (which tend to agglomerate in centre zone of samples) during the first solidification in shot sleeve, thus reducing the microstructural inhomogeneity. Mg addition shifts the eutectic point to lower Mg2Si concentration and induces a slower eutectic growth rate, causing a lower Mg2Si volume fraction in Al–Mg2Si eutectic cell. On the contrary, Si addition increased the Mg2Si volume fraction in eutectic cell by raising the Mg2Si eutectic concentration and the eutectic growth rate. To minimize the interfacial energy, Al–Mg2Si eutectics with different Mg2Si volume fractions exhibit various morphologies. The tensile test results show that both Mg and Si improved the strength at the cost of ductility. However, due to the formation of fine Al–Mg2Si eutectics, Si induced less ductility sacrifice than Mg when achieving the same strength improvement.

Ti2Nb2xO4+5x compounds are very popular negative-electrode materials for lithium-ion batteries due to their high specific capacities, safe operating potentials and high cycling stability. Nevertheless, their poor electronic conductivities and insufficient Li+ diffusion coefficients limit the rate capabilities. Herein, we explore highly conductive CrNb11O29 with a high theoretical capacity (401 mAh g−1) and an open Wadsley–Roth shear structure as a new intercalating negative-electrode material having the same advantages of Ti2Nb2xO4+5x but a high rate capability. CrNb11O29 nanorods (CrNb11O29-R) with lengths of 500–1000 nm and very small diameters of 30–50 nm are prepared based on a novel hydrothermal method. Due to the free electrons in Cr-3d orbitals and the large ionic radius of Cr3+, CrNb11O29 exhibits a high electronic conductivity and large Li+ diffusion coefficients, respectively. In-situ X-ray diffraction analyses confirm its high structural stability. These conductivity, structural and architectural advantages in CrNb11O29-R lead to its significant pseudocapacitive contribution (82.0% at 1.1 mV s−1), prominent rate capability (high reversible capacities of 343 mAh g−1 at 0.1C and 228 mAh g−1 at 10C), and outstanding cycling stability (only 8.9% capacity loss at 10C over 400 cycles).

M–Nb–O compounds are advanced anode materials for lithium-ion batteries (LIBs) due to their high specific capacities, safe operating potentials, and high cycling stability. Nevertheless, the found M–Nb–O anode materials are very limited. Here, Mg2Nb34O87 is developed as a new M–Nb–O material. Mg2Nb34O87 porous microspheres (Mg2Nb34O87-P) with primary-particle sizes of 30–100 nm are fabricated based on a solvothermal method. Mg2Nb34O87 has an open 3 × 4 × ∞ Wadsley–Roth shear structure and a large unit-cell volume, leading to its largest Li+ diffusion coefficients among all the developed M–Nb–O anode materials. In situ X-ray diffraction analyses reveal its high structural stability and intercalating characteristic. These architectural, conductivity, and structural advantages in Mg2Nb34O87-P lead to its most significant intercalation pseudocapacitive contribution (87.7% at 1.1 mV s–1) among the existing M–Nb–O anode materials and prominent rate capability (high reversible capacities of 338 mAh g–1 at 0.1C a...

The formation, 3D morphology and growth mechanism of the Al6(Fe, Mn) phase were studied in Al–Mg–Mn–Fe alloys processed using high pressure die casting (HPDC). Thermodynamic calculations and the observed microstructures indicate that the Al6(Fe, Mn) phase in the HPDC Al–Mg–Mn–Fe alloys is a dominant metastable phase in phase competition with the stable Al13(Fe, Mn)4 phase. The experimental results confirm that Mn addition in the alloy suppresses the transformation from the metastable Al6(Fe, Mn) phase to the stable Al13(Fe, Mn)4 phase under non-equilibrium solidification conditions. Energy-dispersive spectroscopy (EDS) analysis of extracted particles reveals that the average Mn/Fe atomic ratio in the Al6(Fe, Mn) phase decreases as the Mn/Fe atomic ratio in the melt decreases. It is also found that the Al6(Fe, Mn) phase grows to form two elongated prism morphologies: rhombic prism (equilibrium morphology, bounded by {110} and {002}), and rectangular prism (growth morphology, bounded by {002}, {200} and {020}). The primary Al6(Fe, Mn) phase shows a hollow structure and the eutectic phase is in the form of fine solid particles. The growth mechanism of the Al6(Fe, Mn) phase is also elucidated according to the crystallographic rules and the morphological characteristics of the Al6(Fe, Mn) phase.

Debate on the accurate heterogeneous nucleus of α-Mg in carbon-inoculated Mg-Al based alloys has lasted for decades, due to the difficulty of phase identification since aluminum carbide readily hydrolyzes. In this paper, a novel Al-3C master alloy was used as the refiner and to reveal the α-Mg nucleating substrate. To avoid hydrolysis, focused Ion Beam (FIB) was used to prepare samples, and Electron Back-Scattered Diffraction (EBSD) phase structure analysis was carried out to identify the phase type of the α-Mg nucleus. The experimental results indicate that a cluster of Al4C3 particles rather than an individual particle acts as the α-Mg nucleus. The attachment of Al8Mn5 particles to Al4C3 particles restricts the nucleation efficiency. Nevertheless, Al4C3 particles which have not been surrounded by Al8Mn5 can still effectively refine α-Mg. Therefore, it is proposed that the addition of Al-3C master alloy can overcome the negative effect of Mn. Moreover, the excellent stability of Al4C3 in Mg-Al based melts contributes to its remarkable refining and fade-resistant abilities.

The effects of Ni on the phases, microstructural evolution, hot tear susceptibility and mechanical properties of Al–6Zn-1.4Mg-1.2Cu alloys fabricated by gravity casting were investigated using X-ray diffraction (XRD), scanning electronic microscopy (SEM), optical microscopy, the N-Tec Hot tear and tensile test. The calculation of phase diagrams (CALPHAD) modelling was also conducted to understand the phase formation of the experimental alloys. The results showed that the secondary phases (including η-MgZn2, S–Al2CuMg and Al3Ni) are mainly distributed at grain boundary, while round S–Al2CuMg particles are also found in α-Al matrix. Ni only exists as Al3Ni with different morphologies and its number density ascends with the increase of Ni content in alloys, which also significantly improves the hot tear resistance. As a result, the increased Ni in the alloys remarkably improves the ultimate tensile and yield strength, while the elongation increases when Ni 0.6 wt%.

A novel high-strength die-cast Al–Si–Cu–Mg alloy has been developed in the present work. Experimental results indicated that the combination of different amounts of θ-Al2Cu and Q-Al5Cu2Mg8Si6 phases could provide a same yield strength but different elongations due to the differences in size and distribution of these two phases. By optimizing the synergistic strengthening of Q-Al5Cu2Mg8Si6 and θ-Al2Cu phases, the balanced strength-ductility trade-off was achieved at 3.0 wt% Cu and 0.9 wt% Mg, offering a yield strength of 225 MPa and an elongation of 4.3% under as-cast condition. Except the normal Q and θ large lamellar or blocks located in α-Al grain boundary, numerous nanoscale Q-Al5Cu2Mg8Si6 precipitates (mostly under 200 nm) were also observed inside the α-Al grains in the newly developed alloy. Thermodynamic calculation was performed using Pandat 2018 software to explain the formation and distribution of strengthening phases. It was found that Q-Al5Cu2Mg8Si6 can be precipitated from (1) the melt directly via liquid-solid reaction and (2) α-Al phase via solid-solid reaction. The nanoscale Q-Al5Cu2Mg8Si6 particles are considered to be precipitated via the latter solid reactions.

Molecular dynamics (MD) simulations are performed to study the freezing process of Al-Si melts on heterogeneous Si substrates in detail. We highlight the inherent nanostructure of both the Si primary phase and the Al-Si binary phase. It is found for the first time that the primary Si phase displays a "pyramidal configuration" when the Al-Si melt congeals. Experimental measurements could also verify our simulation results. It can be found that the binary Al-Si phase turns into a "Si-Al-Si sandwich construction" during solidification, regardless of freezing on a single substrate or in the restricted space between substrates. This peculiar phenomenon results from the combined effects of the van der Waals potential well and the interatomic interaction between Al and Si. Furthermore, it is also able to control the thickness of the Si atomic shell of the "sandwich construction", resulting in the silicene-like unilaminar Si nanostructure. Our findings provide novel strategies to fabricate desired shaped nanostructures by means of nanocasting in Al-Si melts at the nanoscale.

A novel Si-18Mn-16Ti-11P master alloy has been developed to refine primary Si to 14.7 ± 1.3 μm, distributed uniformly in Al-27Si alloy. Comparing with traditional Cu-14P and Al-3P, Si-18Mn-16Ti-11P provided a much better refining effect, with in-situ highly active AlP. The refined Al-27Si alloy exhibited a CTE of 16.25 × 10−6/K which is slightly higher than that of Sip/Al composites fabricated by spray deposition. The UTS and elongation of refined Al-27Si alloy were increased by 106% and 235% comparing with those of unrefined alloy. It indicates that the novel Si-18Mn-16Ti-11P alloy is more suitable for high-Si Al-Si alloys and may be a candidate for refining hypereutectic Al-Si alloy for electronic packaging applications. Moreover, studies showed that TiP is the only P-containing phase in Si-18Mn-16Ti-11P master alloy. A core-shell reaction model was established to reveal mechanism of the transformation of TiP to AlP in Al-Si melts. The transformation is a liquid-solid diffusion reaction driven by chemical potential difference and the reaction rate is controlled by diffusion. It means sufficient holding time is necessary for Si-18Mn-16Ti-11P master alloy to achieve better refining effect. Keywords: Hypereutectic Al-Si alloy, Primary Si, Refinement, AlP, Thermal expansion behavior, Si-18Mn-16Ti-11P master alloy

The effect of Fe and Mn on the microstructure and mechanical properties of a series of Al-5 wt%Mg alloys processed by high pressure die casting (HPDC) was investigated. The Calculation of Phase Diagrams modelling (CALPHAD) was also carried out to understand the phase formation in experimental alloys. The results show that Fe can be a beneficial element in the Al-Mg and Al-Mg-Mn alloys to improve the mechanical properties. Fe only exists in the form of equilibrium Al13Fe4 phase in Al-Mg-Fe alloys. While, the addition of 0.6 wt%Mn suppresses the formation of equilibrium Al13Fe4 phase. In Al-Mg-Mn-Fe alloys, all Fe-rich intermetallics are Al6(Fe, Mn) phase when Fe level is less than 2.5 wt%. When further increasing the Fe level, the primary non-equilibrium Al6(Fe, Mn) phase gradually evolves to form equilibrium Al13Fe4 phase, but the eutectic phase is still Al6(Fe, Mn). It was also found that both the eutectic Al13Fe4 in Al-Mg-Fe alloys and eutectic Al6(Fe, Mn) in Al-Mg-Mn-Fe alloys are divorced from α-Al phases as the primary Fe-rich phases appear. The Fe-rich intermetallics significantly affect the mechanical properties of experimental alloys. Fe enhances the yield strength obviously but reduces the elongation significantly. The ultimate tensile strength is also improved by Fe addition when Fe level is less than 2.0 wt%, but it is significantly decreased with further increasing the Fe level. Moreover, the Mn addition is found to increase the volume of strengthening Fe-rich intermetallic and thus can further strengthen Al-Mg alloys.