Intermediate Alloy Research Articles

Study on grain refinement of AlB2 structure in aluminium alloys

ABSTRACT Aiming at the problem of unclear grain refinement mechanism in aluminium alloys, Al n B n (n = 2–12) clusters and Al–3B alloy were studied by density functional theory methods. The results show that as the cluster size increased, B atoms self-aggregated, and Al atoms surrounded the surface of the clusters. In addition, Al and B atoms formed stable AlB2 triangular structures. The average binding energy gradually increased with increasing clusters size, which indicated that the clusters structures were gradually stable. Range of n = 2–11, the Al9B9 cluster showed the most stable structure. Electronic properties and interatomic interactions calculation results suggested that there was a minimum electrostatic potential point on the surface of the B atom, and the B atom in AlB2 may be the adsorption site of α-Al. The ab initio molecular dynamics simulations results of the Al–3B alloy showed that Al and B generated the AlB2 structure in situ, and Al atoms nucleated and grew on the AlB2 surface. These results can be used to understand the grain refinement mechanism of the Al–B intermediate alloy.

Study on the Refining Behavior of Al-Si Alloys Doped with Al-Ti-C Intermediate Alloys at Different B Doping Temperatures

In this paper, a novel Al-5Ti-0.3C-0.2B intermediate alloy with an efficient refining effect on Al-Si alloys by a low-cost and high-performance fabrication process is developed. The results show that the addition of only 0.15 wt.% of Al-5Ti-0.3C-0.2B intermediate alloy is able to refine the average grain size of Al-Si alloys to 120 ± 5 μm, which is 28.7% higher than the reference value of 0.2 wt.% addition. Additionally, TiAl3 in bulk form has a faster response and more stable refinement than TiAl3 in needle form. The blocky TiAl3 generated at low temperature will turn acicular or elongated as the temperature increases, slowing the response speed and increasing the time required to achieve the ideal refinement effect. We are convinced that this work will provide a reference for developing new aluminum alloy refinement intermediate alloys.

Study on the Effect of Al-10Sr Intermediate Alloy on the Modification of A356 Aluminum Alloy after Different Purification Treatments

Abstract For three different purification treatment methods of aluminum melt: untreated (UT), conventional purification treatment (CPT), impurity removal flux purification treatment (IRF), and Al-10Sr intermediate alloy was applied for modification treatment. The results showed that due to the highest purity of aluminum liquid treated with IRF, the secondary dendrite spacing decreased by 31.32% after modification, and the eutectic silicon phase was in a granular and dispersed distribution. The tensile fracture exhibited ductile fracture characteristics, effectively improving the mechanical properties of the alloy. At the same time, it was found that reducing the Sr content did not decrease the modifying effect, indicating good purity of aluminum liquid can provide superior melt conditions for subsequent modification treatment.

Weak strain-rate sensitivity of hardness in the VCoNi equi-atomic medium entropy alloy

In this study, high strain rate nanoindentation was utilized to elucidate the dynamic behavior and the underlying deformation mechanisms of the equi-atomic vanadium-cobalt-nickel (VCoNi) medium entropy alloy. The hardness at high strain rate (average indentation strain rate: ∼11,000 s−1) exceeded that at low strain rate (constant indentation strain rate: 0.01 s−1) by only ∼3.5 %. Planar slip was identified as the predominant deformation mechanism at both strain rates, with no evidence of deformation twinning or phase transformation. The low strain rate sensitivity of VCoNi can be attributed to its lower lattice friction relative to that of conventional BCC metals and limited dislocation-dislocation interaction compared to that in typical FCC metals. The low strain rate sensitivity observed in VCoNi may also extend to other intermediate stacking fault energy alloy systems in which planar slip is prevalent.

Phase Transformation of AlV55 Alloy at High Temperature

Vanadium–aluminum alloy is an important intermediate alloy for preparing aviation grade titanium alloys, and its product quality directly affects the finished product quality of titanium alloys. In this study, focusing on the problems of high powder content (19.8%) and low product yield in AlV55 alloy products, we conduct research on alloy quality control technology and implement a vanadium–aluminum alloy cooling crystallization control process. The research results indicate that there are three phases in AlV55 alloy, namely Al8V5, AlV, and Al2V3 phases. As the temperature decreases, the AlV phase gradually decomposes into Al8V5 phase and Al2V3 phase, and the proportion of Al8V5 phase is positively correlated with the fineness. Rapid cooling can reduce the formation of Al8V5 phase. The experimental results show that high-temperature water quenching can increase the proportion of vanadium–aluminum solid solution phase in the alloy from 19.03% to 31.76%, and reduce the fine powder rate to 13.2%, providing important product quality control means and technical support for the production of vanadium–aluminum alloys.

Effect of Si and Holding Time on Ti2Al20La Phase in Al-Ti-La Intermediate Alloy.

The effects of holding time and Si on the content, shape size and structure of Ti2Al20La phase in Al-Ti-La intermediate alloy were investigated by an X-ray diffractometer, scanning electron microscope and transmission electron microscope. The results show that the volume fraction and aspect ratio of Ti2Al20La phase in Al-Ti-La intermediate alloy decrease significantly, from 21% and 2.3 without Si addition to 4% and 2.0 with the addition of 2.3 wt.% Si at a holding time of 15 min at 750 °C, respectively. The Si element will attach to the Ti2Al20La phase and form La-Si binary phase at the grain boundary of α-Al. With the increase of holding time from 15 min to 60 min, the content of Ti2Al20La phase in the alloy gradually decreases and the size decreases significantly. Meanwhile, Al11La3 will dissolve and disappear, while the content of La-Si binary phase increases, and part of Ti2Al20La phase transforms into Ti2(Al20-x,Six)La phase.

Insights into the effects of La on the grain refinement and mechanical properties of Al-Ti-C intermediate alloy and pure Al: A first-principle study and experimental investigation

This paper employs the self-propagating high-temperature synthesis (SHS) to prepare Al-Ti-C master alloys and explores the effects of integrating the rare earth element lanthanum to create Al-Ti-C-La composites. This research focuses on the microstructural changes in both the master alloy and pure aluminum, which aimed to elucidate the mechanisms that enhance grain refinement and resistance to grain refinement fading. The analysis reveals that when Al-Ti-C-La master alloys are incorporated into molten Al, the predominant structures formed include an Al matrix, rod-like Al3Ti phases, and TiC particles, alongside AlLa phases and substantial Al20Ti2La compounds. The grain refining capability of Al-Ti-C-La master alloys is significantly exceeds that of the Al-Ti-C master alloys. The addition of La markedly reduces the settling of TiC particles, thereby granting the Al-Ti-C-La master alloys excellent resistance to grain refinement fading. The newly formed Al20Ti2La phase plays a crucial role in refining the aluminum matrix, with metallic bond characteristics present on the side towards the Al matrix at the Al20Ti2La/Al interface and distinct covalent bond characteristics on the Al20Ti2La side. Moreover, the Al20Ti2La (110)/Al (110) interface exhibits the highest interfacial adhesion energy and stronger covalent bond features. Consequently, α-Al is prone to heterogeneously nucleate on the Al20Ti2La phase via the Al20Ti2La (110)/Al (110)-HCP orientation, which refines the grains of the aluminum matrix, ultimately enhancing the performance of aluminum-based alloys.

Effect of Al–5Ti–1B–La intermediate alloy on microstructure and mechanical properties of A356.2 aluminum alloy

This study delves into the effects of Al–5Ti–1B–1La intermediate alloy, a newly developed refinement agent, on the microstructure and mechanical properties of A356.2 aluminum-silicon alloy modified by Al–10Sr. The decomposition of Ti2Al20La, where La element was concentrated in the Al–5Ti–1B–1La intermediate alloy, hardly affected the conventional nucleation mechanism of TiAl3–TiB2; nonetheless, the La element significantly refined the dendritic arms of α-Al. Notably, the secondary dendrite arm spacing was reduced from 49 μm to 27 μm, when 0.025 wt% ∼0.2 wt% Al–5Ti–1B–1La intermediate alloy and 0.014 wt% Al–10Sr modifier was incorporated to the A356.2 aluminum alloy. Although the room-temperature ultimate tensile strength was increased only by 30 MPa, the elongation was remarkably improved from 10% to 26%. The hardness of the alloy was also enhanced from 75 HBW to 84 HBW. The experimental outcomes underscore the efficacy of minimal La element incorporation in enhancing the performance of Al–5Ti–1B intermediate alloy, and the findings are significant for improving the serviceability of automobile wheels made from A356.2 aluminum alloy. The method used in this study can also be employed to regulate the microstructure and enhance mechanical properties of other sub-eutectic aluminum-silicon alloys.

Microstructure and Properties of Al-Cu-Fe-Ce Quasicrystalline-Reinforced 6061 Aluminum Matrix Composites after Aging

Al-Cu-Fe-Ce quasicrystalline-reinforced 6061 aluminum matrix composites were prepared through hot press sintering and treated with a solid solution and aging treatments. The influence of the solid solution and aging treatments on the microstructure and mechanical properties of the composites was investigated by XRD, EDS, SEM, and TEM. The results show that using Al-Cu-Fe-Ce quasicrystalline intermediate alloy as the reinforcing phase increases the interfacial areas of the composites and enhances the grain boundary strengthening effect, which is conducive to the improvement of the mechanical properties of the composites. And through the solid solution and aging treatment, the β phase and the Al2CuMg phase belonging to the orthorhombic crystal system, as well as the β″ phase and a small amount of the β′ precipitated phase, were formed in aluminum matrix composites, and these precipitated phases all existed in the composites in a fine and uniform distribution, which ensured the consistency of the mechanical properties of the materials and improved the mechanical properties of the composites. Meanwhile, the deficiency of quasicrystalline particle-reinforced 6061 aluminum matrix composites in age-hardening was solved and the age-hardening capability of the composites was further developed. This method provides a feasible process route for the preparation of high-performance aluminum matrix composites. The application of this process is expected to improve the mechanical properties and durability of this composite and offer a more reliable option for the application of aluminum matrix composites in aerospace, transportation, and other fields.

Effect of Al-Sr-Y intermediate alloy on microstructure and mechanical properties of A356 alloy

In this experiment, an intermediate alloy (Al-3Sr-8Y) that can refine and modify A356 alloy simultaneously was developed, and the synergistic effect of Sr and Y on the microstructure and mechanical properties of A356 alloy was investigated. The results show that when the content of Al-3Sr-8Y intermediate alloy reaches 0.3 wt%, the morphology of α-Al dendrites is significantly refined and the secondary dendrite arm spacing (SDAS) was significantly reduced. Moreover, the morphology of eutectic Si transforms from acicular to small fibrous, and the average area and aspect ratio of eutectic Si decrease to 0.81 μm2, and 2.01. This change is caused by the twin plane re-entrant edge (TPRE) poisoning mechanism, where the addition of Al-3Sr-8Y can poison the intrinsic growth position of the Si phase, reduce the growth rate of the Si phase, promote isotropic growth, and achieve a highly branched morphology of the Si phase to form a fibrous structure. Due to the excellent synergistic effect of Sr and Y, the tensile strength and elongation of the alloy reached the maximum values of 303.5 MPa and 9.5% when 0.3 wt% Al-3Sr-8Y was added after heat treatment, which is an increase of 18.2% and 86.3% compared with the untreated A356 alloy, respectively.

Electrochemical formation and characterization of Ni-Sc intermetallic compounds in LiF-CaF2 eutectic melt

The present investigation aimed to examine the cathodic behavior of Sc(III) on a reactive nickel electrode within a fluoride molten salt system. The electrochemical formation process of Ni-Sc alloy in LiF-CaF2 eutectic melt was investigated using cyclic voltammetry and square wave voltammetry electrochemical techniques. The formation of Ni-Sc intermetallic compounds induces a depolarization phenomenon, hence promoting the underpotential deposition of scandium onto the Ni electrode. The standard Gibbs free energy of formation for Ni-Sc intermetallic compounds were calculated by the use of open-circuit chronopotentiometry measurements. Furthermore, Ni-Sc alloys were fabricated via potentiostatic and galvanostatic electrolysis methods and subsequently characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The results indicated that a sequential emergence of Ni5Sc, Ni2Sc, and combined NiSc+NiSc2 intermetallic compounds escalates as the cathodic polarization potential. Multifarious Ni-Sc intermetallic compounds can be synthesized by controlling the electrolysis conditions, providing new insights for the preparation of Ni-Sc alloy and establishing a theoretical foundation for the synthesis of Ni-Sc intermediate alloy for solid-state reactive cathodes.

Unleashing the Potential of High-Capacity Anodes through an Interfacial Prelithiation Strategy.

The scalable development of an environmentally adaptive and homogeneous Li+ supplementary route remains a formidable challenge for the existing prelithiation technologies, restricting the full potential of high-capacity anodes. In this study, we present a moisture-tolerant interfacial prelithiation approach through casting a hydrophobic poly(vinylidene-co-hexafluoropropylene) membrane blended with a deep-lithiated alloy (Li22Si5@C/PVDF-HFP) onto Si based anodes. This strategy could not only extend to various high-capacity anode systems (SiOx@C, hard carbon) but also align with industrial roll-to-roll assembly processes. By carefully adjusting the thickness of the prelithiation layer, the densely packed Si@C electrode (4.5 mAh cm-2) exhibits significantly improved initial Coulombic efficiency until a close-to-unit value, as well as extreme moisture tolerance (60% relative humidity). Furthermore, it achieves more than 10-fold enhancement of ionic conductivity across the electrode. As pairing the prelithiated Si@C anode with the LiNi0.8Co0.1Mn0.1O2 cathode, the 2 Ah pouch-format prototype balances an energy density of ∼371 Wh kg-1 and an extreme power output of 2450 W kg-1 as well as 83.8% capacity retention for 1000 cycles. The combined operando phase tracking and spatial arrangement analysis of the intermediate alloy elucidate that the enhanced Li utilization derives from the gradient stress dissipation model upon a spontaneous Li+ redistribution process.

Thermal stability study of gallium nitride based magnetic field sensor

We investigated the thermal stability and performance of AlGaN/AlN/GaN Hall-effect sensors under industry-relevant atmospheric conditions. The thermal stability and performance of Hall sensors are evaluated by monitoring Hall sensitivity, two-dimensional electron gas density, and Ohmic contact resistance during aging at 200 °C for up to 2800 h under atmospheric conditions. This was accomplished by characterizing AlGaN/AlN/GaN micro-Hall sensors, with and without contacts, and before and after being placed under different thermal aging times. Observed electrical performance was correlated with the micro-structural evolution of AlGaN/AlN/GaN Hall sensor heterostructures. Results indicate that the AlGaN/AlN/GaN Hall sensor provides stable performance for as long as 2800 h aging at 200 °C without any significant degradation of (i) Hall sensitivity, (ii) two-dimensional electron gas, and (iii) Ohmic contacts. However, there was a small change in sheet density and mobility, which is due to a decrease in polarization, resulting from local inhomogeneous strain relief at the barrier layer. During the early stage of thermal aging, a decrease in contact resistance was also observed and attributed to (i) out-diffusion of “Ga” at the vicinity of the contact interface, and (ii) a reduction in oxygen concentration and formation of Al–Ti intermediate alloy at the GaN/Ti interface, resulting in a reduced barrier and enhanced electron transport at the contacts. However, despite these small changes, results indicate that the AlGaN/AlN/GaN Hall sensor provides stable performance for as long as 2800 h thermal aging at 200 °C.

Effects of Cold Rolling Reduction Rate on the Microstructure and Properties of Cu-1.16Ni-0.36Cr Alloy after Thermo-Mechanical Treatment.

In this paper, a Cu-Ni-Cr alloy was prepared by adding a Ni-Cr intermediate alloy to copper. The effects of the cold rolling reduction rate on the microstructure and properties of the Cu-1.16Ni-0.36Cr alloy after thermo-mechanical treatment were studied. The results show that the tensile strength of the alloy increased while the electrical conductivity slightly decreased with an increase of the cold rolling reduction rate. At a rolling strain of 3.2, the tensile strength was 512.0 MPa and the conductivity was 45.5% IACS. At a rolling strain of 4.3, the strength further increased to 536.1 MPa and the conductivity decreased to 41.9% IACS. The grain size and dislocation density decreased with an increase of the reduction rate in the thermo-mechanical treatment. However, when the rolling strain reached 4.3, the recrystallization degree of the alloy increased due to an accumulation of the dislocation density and deformation energy, resulting in a slight increase in the grain size and a decrease in the dislocation density. The texture strength of the brass increased due to the induced shear band, with an increase of the cold rolling reduction rate. The reduction rate promoted a uniform distribution of nano-scale Cr precipitates and further enhanced the strength via precipitation strengthening.

Experimental and quantum chemical investigations on the generation mechanism of Al-V intermediate alloy by aluminothermic reduction of NaVO3

In the present study, the reaction process and reaction mechanism of the aluminothermic reduction of NaVO3 to prepare aluminum-vanadium intermediate alloy were investigated by experimental analysis and quantum chemical calculations. The results of thermal analysis and isothermal experiments indicated that the aluminothermic reduction of NaVO3 was a multi-step process and temperature played a critical role in this process. The aluminum-vanadium intermediate alloy was generated when the temperature exceeded 963 ºC, and it could be further separated from the reduction product after the addition of slag-forming agents (CaO and CaF2) at 1600 ºC. Furthermore, an atomic-level insight into the reaction between aluminum and NaVO3 was explored based on the electrostatic potential (ESP) analysis of the reactivity of NaVO3. The results showed that the aluminum atom first interacted with NaVO3 to form an intermediate complex through electrostatic interaction, and then NaVO3 was reduced to NaVO2 under the continuous action of aluminum. Further, the newly formed NaVO2 was consequently converted to aluminum-vanadium intermediate alloy under the continuous action of aluminum atoms. These theoretical results were essentially consistent with the experimental data, which provided a fundamental understanding about the reaction mechanism of NaVO3 with Al. Moreover, the aluminothermic reduction of NaVO3 also provided a feasible and environmentally friendly metallurgical approach for preparing aluminum-vanadium intermediate alloy.

Local structures and undercooling ability of Zr–Ti melts

We developed an accurate model of Zr–Ti melts for classical molecular-dynamics simulations via regauging the existing embedded-atom method (EAM) potential, using particularly the diffusion coefficient data obtained from quasielastic neutron scattering. This EAM potential well reproduces the properties of the melts observed in experiments, including mass density, transport coefficients, melting temperatures, and static structure factors. The latter are also obtained from ab initio simulations. Using the developed EAM potentials, we analyzed the short-range order of the liquids and found a chemically preferred formation of Zr–Zr and Zr–Ti nearest neighbor pairs. When decreasing the temperature the number of icosahedral-like aggregates increases on the expense of more crystal-like structures. This is most pronounced at intermediate alloy compositions. At intermediate compositions also the lowest thermodynamic driving force for crystallization is found, resulting in the largest undercooling ability of the alloys.

Deuterium permeation through liquid tin supported by a nickel substrate

A model of deuterium permeation through liquid (liq.) Sn supported by a nickel (Ni) substrate is proposed as follows; deuterium dissolves in liq. Sn according to the Sieverts’ law and its concentration immediately becomes uniform through the liq. Sn layer due to large diffusivity of deuterium in liq. Sn. A thin intermediate Sn-Ni alloy layer is formed at an interface of liq. Sn and the Ni substrate in a transient of deuterium permeation. Deuterium concentration and diffusivity in the alloy layer would be lower than those in liq. Sn and pure Ni, resulting in lower deuterium permeability. Consequently, the intermediate Sn-Ni alloy layer could control total deuterium permeation through the liq. Sn supported by the Ni substrate.

Clean separation of vanadium from NaVO3 in NaF-KF-AlF3 molten salt by electrochemical reduction

Aluminum-vanadium intermediate alloy is a significant raw material for the fabrication of high-performance titanium alloys. In the present study, the electrochemical behavior of NaVO3 on a solid molybdenum and liquid aluminum electrode is systematically investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV) in the NaF-KF-AlF3 molten salt and the formation mechanism of Al-V intermetallic compounds is emphatically analyzed. The results show that the electrochemical reduction of VO3− on the solid molybdenum electrode is a multi-step process and low-valence vanadium oxide (V2O3) is obtained. In contrast, the electrochemical reduction of VO3− to V2O3 on liquid aluminum electrode is through one-step process and the deposition potential is more positive than that on molybdenum electrode owing to the depolarization effect of the liquid aluminum electrode. In addition, Al-V intermetallic compounds are obtained on the liquid aluminum electrode by potentiostatic electrolysis. The reduction process of VO3− on the liquid aluminum electrode is described as: the electrochemical process is started by the direct electro-reduction of VO3− to V2O3, which is further converted to Al-V intermetallic compounds under the combined effect of electrochemical and aluminothermic reduction, with the latter playing a dominant role.

Real-Time Diagnostics of 2D Crystal Transformations by Pulsed Laser Deposition: Controlled Synthesis of Janus WSSe Monolayers and Alloys

Energetic processing methods such as hyperthermal implantation hold special promise to achieve the precision synthesis of metastable two-dimensional (2D) materials such as Janus monolayers; however, they require precise control. Here, we report a feedback approach to reveal and control the transformation pathways in materials synthesis by pulsed laser deposition (PLD) and apply it to investigate the transformation kinetics of monolayer WS2 crystals into Janus WSSe and WSe2 by implantation of Se clusters with different maximum kinetic energies (<42 eV/Se-atom) generated by laser ablation of a Se target. Real-time Raman spectroscopy and photoluminescence are used to assess the structure, composition, and optoelectronic quality of the monolayer crystal as it is implanted with well-controlled fluxes of selenium for different kinetic energies that are regulated with in situ ICCD imaging, ion probe, and spectroscopy diagnostics. First-principles calculations, XPS, and atomic-resolution HAADF STEM imaging are used to understand the intermediate alloy compositions and their vibrational modes to identify transformation pathways. The real-time kinetics measurements reveal highly selective top-layer conversion as WS2 transforms through WS2(1-x)Se2x alloys to WSe2 and provide the means to adjust processing conditions to achieve fractional and complete Janus WSSe monolayers as metastable transition states. The general approach demonstrates a real-time feedback method to achieve Janus layers or other metastable alloys of the desired composition, and a general means to adjust the structure and quality of materials grown by PLD, addressing priority research directions for precision synthesis with real-time adaptive control.

Preparation of high-quality FeV50 alloy by an improved SHS-EAH multi-stage process

As the most widely used vanadium intermediate alloy, ferrovanadium is mainly prepared by the self-propagating high-temperature synthesis (SHS) process with the advantages of short process and large heat release. However, there is a trade-off between the amount of reduction agent of Al and the product quality of ferrovanadium, which is caused by the thermodynamic equilibrium limitation of the reduction between Al and vanadium oxides. The reasonable adjustment of the trade-off has become an urgent problem to be solved for the preparation of high-quality ferrovanadium. In the present work, the thermodynamic equilibrium for the reduction limitation using Al as reducing agent has been thoroughly analyzed with the reference to the equilibrium phase diagram. It was found that the theoretical reduction limitation of total vanadium (T.V) in slag was decreased from 4.08 wt.% to wt. 0.86 wt.% when the Al content in alloy reached 2.0 wt.% at 1800 °C. The vanadium in slag was mainly presented in the form of MgV3O8 and coexisting with other phases of MgAl2O4, CaAl2O4, CaAl4O7, CaAl12O19. With the purpose of further decrease the high Al concentration in alloy and vanadium loss in slag, an improved SHS-EAH process was implemented by multi-stage gradient aluminum addition coefficient pattern, the average vanadium content in slag was reduced from 1.82 wt.% to 0.83 wt.%, while the aluminum content in FeV50 alloy was decreased from 1.5 wt.% to 0.4 wt.%. The SHS-EAH process was proved to be a better process with improved yield and quality for the preparation of ferrovanadium.