Al3 Sc Research Articles

Tailored Mechanical and Conductive Properties of Continuous Rheo-Extruded Al–Sc–Zr Alloy Conductors by Thermomechanical Treatment

Tailored Mechanical and Conductive Properties of Continuous Rheo-Extruded Al–Sc–Zr Alloy Conductors by Thermomechanical Treatment

Stimulated heterogeneous distribution of Sc element and its correlated local hardening effect in Al–Fe–Ni-Sc alloy

This work studied the stimulated heterogeneous distribution behavior of Sc element and the correlated local hardening effect in the eutectic Al–Fe–Ni alloy. Through microstructure characterizations, Sc was found to aggregate along grain boundaries, namely eutectic phase free areas. The aggregation behavior made the Sc concentration in eutectic phase free areas reach even twice of nominal addition, which was more uneven than Sc in Al–Sc alloy. Meanwhile, tiny Al grains were induced in eutectic phase free areas when the Sc addition exceeded 0.3 wt%. These stimulated heterogeneous distribution behaviors were attributed to solute redistribution exacerbated by the eutectic structure, and discussed by a modified Scheil Equation analytically. Furthermore, nanoindentation tests demonstrated a local hardening behavior correlated with the stimulated heterogeneous distribution of Sc element. Through a quantitatively explanation, it was finally concluded that the inhomogeneous distribution of Sc element can effectively induce the strengthening effect to the eutectic alloy at macro scale.

Hardening behavior of Al-0.25Sc and Al-0.25Sc-0.12Zr alloys during isothermal annealing

The hardening behavior of Al-0.25Sc and Al-0.25–0.12 (wt.%) alloys during isothermal annealing were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), optical microscopy (OM), and hardness measurements. The results show that Sc-containing aluminum alloy contained fine dispersion of spherical secondary Al3Sc particles, which developed during the annealing process. Al3(Sc, Zr) precipitates in the Al-0.25Sc-0.12Zr alloys are core-shell structure. Different isothermal annealing temperatures can lead to different strengthening effects on the alloys. Al-0.25Sc and Al-0.25Sc-0.12Zr alloys both exhibit obvious annealing hardening behavior, and the ternary Al-0.25Sc-0.12Zr alloy shows better thermal stability than Al-0.25Sc alloy.

Precipitation sequence in Al–Mg–Si–Sc–Zr alloys during isochronal aging

6xxx-series Al alloys are the most commonly used alloys in the automotive industry as they have an appropriate balance of strength, corrosion resistance and formability. These alloys experience significant strengthening from the precipitation of coherent GP-zones and β'' precipitates. One opportunity to achieve stronger 6xxx-series Al alloys, without affecting corrosion and formability, is the use of Sc. The strengthening benefits from Sc are obtained by the formation of the Al3Sc dispersoids. The addition of Zr, together with Sc, results in the formation of hybrid Al3(Sc,Zr) dispersoids with a core–shell morphology. The microstructural development in 6xxx-series alloys containing Sc is still largely unknown. Here we show, that combining conductivity, hardness and modelling allows for the prediction of the precipitation sequence in an Al–Sc–Zr, an Al–Mg–Si and an Al–Mg–Si–Sc–Zr alloy. The evolution of conductivity and hardness during isochronal aging is discussed in terms of solute depletion and precipitate formation. APT, TEM and SEM are also conducted in key conditions to help interpret the resistivity and hardness fluctuations. Modelling allows for estimation of the precipitation kinetics of the Mg-Si precipitates and Sc–Zr dispersoids during isochronal aging. The precipitation kinetics of Al3(Sc,Zr) is found to be accelerated in the presence of Mg and Si and APT reveals that this is due to the preferred nucleation of the Al3(Sc,Zr) dispersoids on the MgSi precipitates. These results pave the way for the design of suitable heat treatments for 6xxx-series alloys containing Sc that would allow for the formation of both Al3(Sc,Zr) dispersoids and fine MgSi precipitates.

Formation of Metastable Aluminides in Al–Sc–Ti (Zr, Hf) Cast Alloys

The effect of the ternary alloys composition and overheating of their melts (at 100–370 K above the liquidus temperature) on the morphology and composition of aluminides in the Al–Sc–Ti, Al–Sc–Zr, Al–Sc–Hf systems were investigated. It was shown that during the crystallization of these melts under certain conditions, the primary precipitated phase are the complex aluminides Al3(ScxZr1−x), Al3(ScxTi1−x), Al3(ScxHf1−x) having a metastable cubic lattice with L12 structure, which matches the α-Al structural type. The variety of growth forms of aluminides is explained by a combination of a number of factors: the magnitude of overheating of the melt, the difference in the diffusion coefficients of transition metals, and the local concentration of transition metals in the respective growth zones.

Mechanical, Thermal and Electrical Characteristics of Conventionally Cast and Cold-Rolled 5754-Sc-Zr Aluminium Alloy

The effect of cold-rolling on mechanical, thermal, and electrical properties as well as microstructure behaviour of the Al-2.93wt.%Mg-0.34wt.%Mn-0.33wt.%Si-0.22wt.%Fe-0.19wt.%Cr-0.24wt.%Sc-0.06wt.%Zr was studied. The material was investigated during step-by-step isochronal annealing in a temperature range from room temperature up to 540 °C and during isothermal annealing at 200, 450 and 550 °C. Precipitation reactions were studied by electrical resistometry, conductivity, (micro) hardness measurements and differential scanning calorimetry. The hardening effect appears due to the additional precipitation of the Al3Sc and/or Al3(Sc,Zr) particles. The distinct changes in residual resistivity ratio above ~ 330 °C are probably caused by precipitation of the Mn (,Fe,Cr)-containing particles. This precipitation process is highly influenced by cold rolling but it has a negligible effect on hardness. The apparent activation energy values for additional formation of the Al3Sc and/or Al3(Sc,Zr) particles were determined. The kinetics of the Al3(Sc,Zr)-phase precipitation seems to be independent of Mn-and Mg-addition in the studied alloys. A partial recrystallization of the cold-rolled alloy was registered by electron backscatter diffraction after annealing at 550 °C. The initial difference in microhardness introduced by cold rolling is almost removed after annealing at 550 °C/30 min.

Quantitative contributions of solution atoms, precipitates and deformation to microstructures and properties of Al–Sc–Zr alloys

Abstract In order to investigate the effects of solid solution atoms, precipitated particles and cold deformation on the microstructures and properties of Al–Sc–Zr alloys, the Al–Sc–Zr alloys prepared by continuous rheo-extrusion were treated by thermomechanical treatment, analyzed for conductivity and mechanical properties by tensile and microhardness testing, and characterized using optical microscope, TEM and STEM. A mathematical model was established to quantitatively characterize the contribution of solid solution atoms, precipitates and cold deformation to the conductivity of the alloy. The results show that the strength of Al alloy can be significantly improved by solid solution, aging and cold deformation, and the quantitative impacts of solution atoms, precipitates and cold deformation on the conductivity of Al alloy are 10.5% (IACS), 2.3% (IACS) and 0.5% (IACS), respectively. Aging and cold deformation treatments are the keys to obtain high-strength and high-conductivity aluminum alloy wires.

Effect of Sc and Zr on Al<sub>6</sub>(Mn,Fe) Phase in Al–Mg–Mn Alloys

The effects of Sc and Zr on the shape, size, and number density of Al6(Mn,Fe) phase in Al–5Mg–0.7Mn alloys were investigated by this article. The results showed that Sc and Zr can form strengthening particles of Al3Sc and Al3(Sc,Zr), which have the effect of refining grains and modifying the morphology and distribution of Al6(Mn,Fe) phase. The OM, SEM, and TEM images indicate that with the formation of primary Al3Sc and Al3(Sc,Zr), the shape of Al6(Mn,Fe) became more regular, size of Al6(Mn,Fe) became smaller, and the number density of Al6(Mn,Fe) increased when compared with base alloy. Zr could motivate the precipitation of primary Al3(Sc,Zr) and Al–5Mg–0.7Mn–0.2Sc–0.2Zr had better refining effect than Al–5Mg–0.7Mn–0.4Sc. The grain refinement and finely dispersed Al6(Mn,Fe) phase can improve the mechanical properties such as yield strength and ultimate tensile strength and the corrosion resistance by the results of intergranular corrosion (IGC) also improved.

Material Parameter Extraction for Complex AlScN Thin Film Using Dual Mode Resonators in Combination with Advanced Microstructural Analysis and Finite Element Modeling

AbstractAccurate property determination of the piezoelectric thin film material Al(1−x)Sc(x)N is necessary for designing the next generation of radio frequency resonators in mobile communication, and for testing results of ab initio calculations. Sound velocity and piezoelectric coupling of both longitudinal and shear mode are evaluated from a single dual mode resonator. This assures a compatible set of coefficients. It is observed that AlScN thin films grew differently on small, isolated bottom electrodes. The investigated film starts growing with a slightly tilted, c‐textured microstructure, and switches after 200 nm to a polycrystalline film with irregularly oriented grains having c‐axis tilt angles in the range of 35°–70°, as revealed by transmission electron microscope nanodiffraction mapping. Based on this information, a finite element model (FEM) is constructed that properly reproduces the resonance behavior of the resonator. The relevant elastic and piezoelectric constants are derived by curve fitting and yield somewhat lower stiffness and higher piezoelectric coefficients than ab initio calculations published in the literature. The FEM modeling results show that the upper film part with the abnormally oriented grains is overall piezoelectric, i.e., the misoriented grains maintain the polarity projected onto the growth direction from the starting layer.

Synthesis of nanoscale spherical TiB2 particles in Al matrix by regulating Sc contents

Abstract

Ambient-temperature mechanical properties of isochronally aged 1420-Sc-Zr aluminum alloy

Ambient-temperature mechanical properties of isochronally aged 1420-Sc-Zr aluminum alloy were investigated. A significant grain refinement is caused with the additions of Sc and Zr. No primary Al3Sc or Al3Zr is found in as-cast 1420-Sc-Zr alloy. However, primary Al3(Sc,Zr) particles exist in as-cast 1420-Sc-Zr alloy. During the isochronal aging process, these particles of Al3Li, Al3Sc and Al3Zr begin to precipitate at 100 °C, 250 °C and 450 °C, respectively. These precipitation particles make 1420-Sc-Zr alloy obtain three peak microhardness: 845 MPa at 150 °C, 1000 MPa at 350 °C, and 985 MPa at 500 °C. The predicted strengthening increments are contrasted to the measured strengthening increment to confirm the operative precipitation mechanism at different isochronal aging. The shearing mechanism is operating in 1420 and 1420-Sc-Zr alloys aged isochronally to 150 °C. A mixed mechanism (the shearing and bypass mechanisms) is predicted to be operative in 1420-Sc-Zr alloy aged isochronally to 350 °C. The Orowan strenthening mechanism is operative in 1420-Sc-Zr alloy aged isochronally to 500 °C. During isothermal aging at 475 °C after aged isochronally to 450 °C, 1420-Sc-Zr alloy exhibits excellent thermal stability.

Ageing Behaviour of Sc-Doped Cu–Zn–Al Shape Memory Alloys

The effect of scandium (Sc), when added in trace, on the ageing behaviour of Cu–Zn–Al shape memory alloy was investigated in the present work. Cu–Zn–Al shape memory alloy was prepared by melting 70:30 brass using commercial grade Cu strips and Al chips. Sc was added using Al–Sc 2 wt% master alloy at the time of melting, and the final composition was adjusted to 0.1 wt% Sc. Chemical composition of the alloys was analysed by using EDAX and spectrometer. The influence of Sc on mechanical properties under different ageing conditions were primarily evaluated by Vickers hardness test. Optical and scanning electron microscopy (SEM) was used to analyse the microstructure. Differential scanning calorimetry was used to measure the transformation temperatures, correspond to martensite to austenite or the reverse transformation. Thermo-Calc software was used to construct a phase fraction diagram as a function of temperature to obtain the evolving phases during quenching and subsequent ageing process for both of the alloy systems. The ageing behaviour was also examined using XRD and SEM characterization and explained in the light of phase predictions obtained from the thermodynamic calculations. Subsequently, transmission electron microscopy investigation was carried out to evaluate the influence of Sc on the size and habit planes of the precipitates in Cu–Zn–Al ternary alloy system. Sc has been found to reduce the transformation temperature and consequently increase the mobility of the martensite/austenite interface.

Structure and growth of core–shell nanoprecipitates in Al–Er–Sc–Zr–V–Si high-temperature alloys

Lightweight Sc-containing aluminum alloys exhibit superior mechanical performance at high temperatures due to core–shell, L12-ordered trialuminide nanoprecipitates. In this study, the structure of these nanoprecipitates was studied, using different transmission electron microscopy (TEM) techniques, for an Al–Er–Sc–Zr–V–Si alloy that was subjected to a two-stage overaging heat treatment. Energy-dispersive X-ray spectroscopy of the spherical Al3(Sc, Zr, Er ,V) nanoprecipitates revealed a core–shell structure with an Sc- and Er-enriched core and a Zr-enriched shell, without a clear V outer shell. This structure is stable up to 72% of the absolute melting temperature of Al for extended periods of time. High-angle annular dark-field scanning TEM was used to image the {100} planes of the nanoprecipitates, demonstrating a homogeneous L12-ordered superlattice structure for the entire nanoprecipitates, despite the variations in the concentrations of solute atoms within the unit cells. A possible growth path and compositional trajectory for these nanoprecipitates was proposed using high-resolution TEM observations, where different rod-like structural defects were detected, which are considered to be precursors to the spherical L12-ordered nanoprecipitates. It is also hypothesized that the structural defects could consist of segregated Si; however, this was not possible to verify with HAADF-STEM because of the small differences in Al and Si atomic numbers. The results herein allow a better understanding of how the Al–Sc alloys’ core–shell nanoprecipitates form and evolve temporally, thereby providing a better physical picture for future atomistic structural mappings and simulations.

The Effect of Sc2O3 on the Physicochemical Properties of Low-Melting Cryolite Melts КF–AlF3 and КF–NaF–AlF3

Quasibinary phase diagrams of the system “low-melting cryolite–Sc2O3” the potential media for synthesizing alloyed alloys Al–Sc are plotted by the method of thermal analysis. The phase diagrams of (KF–NaF–AlF3)–Sc2O3 with different content of NaF and the cryolite ratio (CR) 1.3 and 1.5 are the diagrams with simple eutectics. The liquidus temperature of the (KF–AlF3)–Sc2O3 system increases with the increase in the Sc2O3 concentration due to the formation of a high-melting compound: potassium hexafluoroscandiate К3ScF6. The solubility of Sc2O3 in low-melting cryolite melts KF–NaF–AlF3 increases with the increase in temperature and CR. In contrast Al2O3, the solubility of Sc2O3 in melts containing KF–AlF3 with CR = 1.3–1.5 is much lower than in cryolite melts containing NaF. The conductivity of low-melting cryolite melts measured by the method of impedance spectroscopy decreases in proportion to the Sc2O3 concentration in the similar way as in salt melts containing Al2O3. Based on the experimental data obtained, the compositions of low-melting cryolite melts are proposed for the synthesis of doped Al–Sc alloys.

Effect of precipitates on properties of cold-rolled Al–Mg–Si–Sc–Zr alloy with higher temperature aging

ABSTRACTThe aging hardening behaviours of the cold-rolled Al–Mg–Si–Sc–Zr alloy were investigated. The microstructure, hardness and electrical conductivity (EC) of the Al–Mg–Si–Sc–Zr alloy were measured. The relationship between the microstructure and the properties of the Al–Mg–Si–Sc–Zr alloy with cold-rolling and aging processes was studied. The result shows that the addition of Sc and Zr elements significantly refines the grains of the Al–Mg–Si alloy during casting. The cold rolling promotes the Al–Sc(Zr) precipitation. The precipitate strengthening increases with increasing roll reduction. The EC of the cold rolling + aging Al–Mg–Si–Sc–Zr alloy increases with increasing rolling reductions. The combination effects of the precipitation hardening and DRX softening during the aging process lead to the similar peak hardness values of around 70 HV of the rolled Al–Mg–Si–Sc–Zr alloy with the different reductions.

FP-LAPW investigation of Al3(Sc1−xTix) alloys properties in L12 and D022 structures

The ab-initio calculations based on the density functional theory (DFT) have been performed to study the structural, mechanical, electronic, thermal and thermodynamic properties of Al3Sc and Al3Ti binary compounds and their ternary mixture Al3(Sc[Formula: see text]Ti[Formula: see text]) in L12 and D0[Formula: see text] structures. The total energy calculations show that the L12 structure is the more stable one. The Al3Sc[Formula: see text]Ti[Formula: see text] undergoes a martensitic transformation and the formation enthalpies and the lattice parameters decrease with increasing concentration x. The elastic constants are determined and the results show that all compounds are mechanically stable and the cubic cells are more easily deformed by shearing than by unidirectional compression. The elastic modulus indicates that the addition of Ti atoms to Al3Sc improves its ductility. The densities of states (DOSs) calculations show the strong spd hybridization which leads to the formation of a pseudo-gap near the Fermi level in ternary alloys. The densities of states at the Fermi level N(E[Formula: see text]) confirm the phase stability. The quasi-harmonic Debye model is used to predict the thermal properties such as heat capacity, Debye temperature, Grüneisen parameter and thermal expansion coefficient of the considered alloys. The determination of Gibbs free mixing energy at different concentrations has been used to calculate the T–x diagram.

Preparation of Aluminum-Scandium Master Alloys by Aluminothermal Reduction of Scandium Fluoride Extracted from Sc2O3

Aluminium alloys containing small additions of scandium exhibit unique operating properties. Alloying material with scandium significantly improves product weldability, reduces the tendency towards hot cracks and improves welded joint mechanical properties. The aim of this work is to increase the scandium extraction into a master alloy by preliminary transformation of scandium oxide into fluoride and introduction into the composition of an aluminium powder alloying additive. Results are provided of laboratory experiments for preparation of aluminium-scandium master alloy by aluminothermic reduction of scandium fluoride using sodium fluoride and aluminium powder within the alloy composition. Scandium fluoride is prepared by treating scandium oxide with 40% hydrofluoric acid. The overall extraction of scandium from oxide into fluoride and from fluoride to the aluminium-scandium master alloy is 88.5% with an average scandium concentration in the master alloy of 1.90 wt.%. The microstructure of the master alloy obtained is represented by scandium aluminide Al3Sc crystals with a size from 10 to 25 μm uniformly distributed within the master alloy. An additional reserve for increasing the extraction of scandium into the master alloy and reducing its cost is processing of slags formed in the preparation of the ligature. The use of an aluminium powder with high specific surface area in the composition of the alloying additive increases scandium extraction into the master alloy due to better contact of the reacting phases. The resultant Al–Sc master alloy has uniform distribution of Al3Sc particles within the volume of the metal.

Extraction of Scandium and Zirconium from Their Oxides during the Electrolysis of Oxide–Fluoride Melts

The main features of scandium and zirconium extraction from their oxides to aluminum during the aluminothermic and electrolytic preparation of Al–Sc and Al–Zr alloys and master alloys in the KF–AlF3, NaF–AlF3, and KF–NaF–AlF3 oxide–fluoride melts with Sc2O3 and ZrO2 additives are studied. The influence of the melt composition and temperature, the synthesis time, the contents of oxides Sc2O3 and ZrO2 in the melts, the mechanical stirring of aluminum, and the cathodic current density on the contents of scandium and zirconium in aluminum and on their extraction from the oxides is determined. The average values of scandium and zirconium extraction are 20–75 and 40–100%, respectively, depending on the synthesis parameters. The electrolytic decomposition of the oxides in the KF–AlF3, NaF–AlF3, and KF–NaF–AlF3 melts results in the enhancement of scandium and zirconium extraction to aluminum. The parameters of the preparation of Al–Sc and Al–Zr alloys and master alloys with the scandium content to 10 wt % and zirconium content to 15 wt % during the electrolysis of oxide–fluoride melts are chosen as a result of the results obtained.

Phase Transformations and Recrystallization in Cold-Rolled Al-Mg-Sc-Zr Alloy Prepared by Powder Metallurgy

The mechanical, thermal and electrical properties and recrystallization behaviour of the cold-rolled AlMgScZr alloy prepared by powder metallurgy were studied. The materials were investigated during isothermal annealing (400 and 550 °C) and during step-by-step linear annealing from room temperature up to 570 °C. The observed results were compared with microstructure observation by transmission electron microscopy and electron diffraction from a previous study of the Al–Mg-based alloys with Sc and Zr. The precipitation sequence of the Al–Mg system and coarsening of the Sc,Zr-containing particles caused electrical and heat flow changes during the annealing. The presence of the Al3(Sc,Zr) particles has an anti-recrystallization effect that prevents recrystallization at temperature minimally up to ~ 400 °C. A partial recrystallization of the alloy was registered after annealing at 550 °C already for 30 min. The cause of the anti-recrystallization effect is precipitation of the Mg-containing particles as follows from a comparison to the alloy without Mg. But the Mg-addition to the Al–Sc–Zr alloy prepared by powder metallurgy has a poorer anti-recrystallization effect than a Mn-addition.

Preparation and Characterization of Sugar Based Catalyst on Various Supports

A novel structured carbon-based acid catalyst was prepared by depositing the carbon precursor onto glass, ceramic and aluminum supports via dip-coating method, followed by carbonization process for converting the d-glucose layer into black carbon char in an inert nitrogen environment at 400 °C. Then, the –SO3H group was introduced into the framework of the carbon char by multiple vapor phase sulfonation. Four different carbonization methods were carried out (dry pyrolysis and hydrothermal carbonization with or without pressurized) in the catalyst preparation while among the carbonization methods, the samples which prepared from dry pyrolysis without pressurized process showed the strong acidity due to highest adsorption of acid group in the catalyst surface although the catalyst attached onto the support was the least compared to other preparation methods. Among the catalysts, the sulfonated carbon-base catalyst that is attached on the ceramic support exhibited the highest aci-dity (1.327 mmol/g) followed by the catalyst deposited on the glass (0.917 mmol/g) and aluminum (0.321 mmol/g) supports. The porous structure of ceramic surface, allowed a better interaction between reactants and –SO3H site in the carbon. Through the FT-IR analysis, it was observed that the functional groups –COOH, –OH, and –SO3H were present in the active sites of the catalysts. The surface areas of glass (Si–SC), ceramic (Ce–SC) and aluminum (Al–SC) catalysts were larger than 1 m2/g, whereas the pore size belongs to macroporous as the average pore size is more than 50 nm. It is also stable within the temperature of 400 °C as there was less than 10% weight loss revealed from the TGA analysis.