Aluminum Scandium Alloy Research Articles

Microstructures and mechanical properties of friction stir welded additively manufactured Scalmalloy®

The development of high-strength advanced additively manufactured (AM) aluminum alloys is driven by the need for weight reduction in complex-shaped structural applications. In this context, heat-treatable aluminum-scandium alloy, known commercially as Scalmalloy®, offers high strength and lightness, also at high temperatures, due to solution strengthening Al3(Sc, Zr) particles. A widespread diffusion of such AM alloy is also related to welding technologies that could preserve its engineered microstructure. This study investigates the microstructural and mechanical properties of butt friction stir welding (FSW) joints of LPBF Scalmalloy® plates under different welding settings. Joint performance was evaluated under quasi-static and cyclic loading conditions. Porosity in Scalmalloy® and welds was assessed using 3D X-ray computed tomography. An aging heat treatment assessed the extent of precipitation hardening in the FSW joints. Results show that metal stirring during FSW notably reduced the intrinsic porosity of Scalmalloy®, decreasing the equivalent pore diameter from about 200 μm to 60 μm in the welded joints. Under quasi-static loading, welded specimens failed at the interface between the thermo-mechanically affected and the stir zones on the advancing side. The aging heat treatment improved the mechanical strength of Scalmalloy® from approximately 400 to 480 MPa, albeit at the expense of ductility (elongation at fracture decreased from 16 to 4%). The higher heat input and stirring developed at a low welding speed reduced lazy S defects but limited the effectiveness of subsequent aging. In fatigue testing, welded joints consistently failed within the aged base material due to the intrinsic porosity of Scalmalloy®.

Study on adsorption of scandium by iminodiacetic acid resin TP207

Abstract Scandium (Sc) is a rare transition metal applied in unique electronic/alloy materials such as magnesium scandium alloy, aluminum scandium alloy, laser glass, superconductors, and electronic components. However, scandium is extremely hard to obtain. In this paper, the iminodiacetic acid resin TP207 was first applied for the recovery of scandium from a hydrochloric acid solution. The adsorption of Sc3+ by TP207 resin was analyzed by SEM-EDS, FT-IR, and XPS. It was found that the best adsorption time was 2 hours with the equilibrium adsorption rate reaching 99%. The saturated adsorption amount of resin was 0.05g/ml. This process involves the ion exchange of scandium ions with sodium ions on the resin and the chemisorption of scandium with the -COO- group. Furthermore, the TP207 resin exhibited a quasi-second-order kinetic mechanism towards Sc3+, which was the rate of adsorption is proportional to the concentration of the reactants. In addition, the adsorption of resin for Sc3+ is an endothermic reaction by calculating the thermodynamic parameters, and there is a 3.6% difference in adsorption efficiency between the two cycle experiments. In a word, the TP207 resin is a very promising adsorbent for Sc beneficiation from the HCl system.

Increased thermal conductivity and decreased electron–phonon coupling factor of the aluminum scandium intermetallic phase (Al3Sc) compared to solid solutions

Aluminum scandium alloys and their intermetallic phases have arisen as potential candidates for the next generation of electrical interconnects. In this work, we measure the in-plane thermal conductivity and electron–phonon coupling factor of aluminum scandium alloy thin films deposited at different temperatures, where the temperature is used to control the grain size and volume fraction of the Al3Sc intermetallic phase. As the Al3Sc intermetallic formation increases with higher deposition temperature, we measure increasing in-plane thermal conductivity and a decrease in the electron–phonon coupling factor, which corresponds to an increase in grain size. Our findings demonstrate the role that chemical ordering from the formation of the intermetallic phase has on thermal transport.

Critical applications of scandium and progress in the extraction of different scandium resources

Scandium can used in unique electronic or alloying materials such as aluminum-scandium alloys, magnesia-scandium alloys, laser glasses, superconductors and electronic components. However, there is no single scandium mine in the world. Scandium is usually associated with other minerals and is found in very low amounts. Therefore, it is very difficult to obtain scandium and it is of great significance to explore the appropriate extraction process for the production of scandium. This paper highlights key applications of scandium, resource characterization, and production advances with less polluting. It provides environmentally friendly methods for improve scandium product recovery, and optimize the existing process.

Preliminary tests on additive-manufactured Al-Sc specimens for the setup of a numerical model for Laser Shock Peening

Aluminum-Scandium alloys offer a great potential in aerospace applications due their high corrosion resistance and improved strength properties. Furthermore, these alloys have been qualified for laser additive manufacturing (AM), producing parts with static strengths rivalling their conventionally manufactured counterparts. However, laser processing also results in large residual stresses that can severely affect fatigue properties and result in geometric distortion. A proven method for reducing the fatigue-related problems in metallic structures is to drive compressive residual stresses into the affected area by means of Laser Shock Peening (LSP). This surface treatment is very effective in bulk structures, improving life performances of fatigue-sensitive aeronautical components, such as jet engines turbine blades or helicopter gearboxes. On the other hand, quite a limited number of studies has been presented on the effect of LSP on fatigue crack growth in thin components and laser AM structures. This work presents first the results of preliminary tensile tests on additive manufactured Al-Sc specimens. The tensile strengths of as-built and heat-treated samples are compared. Then, a reliable and computationally time-effective numerical model of laser peening is reviewed, referring to case studies investigated earlier. In view of applying LSP to additive manufactured Al-Sc components, the effects of different laser parameters and geometries are discussed. Finally, the possible drawbacks of the LSP treatment are addressed, in order to exploit its full potential in increasing the fatigue life of AM components.

Determination of Trace Thorium and Uranium Impurities in Scandium with High Matrix by ICP-OES.

High-purity scandium oxide is the principal raw material of high-purity scandium metal and aluminum scandium alloy targets for electronic materials. The performance of electronic materials will be significantly impacted by the presence of trace amounts of radionuclides due to the increase in free electrons. However, about 10 ppm of Th and 0.5-20 ppm of U are typically present in commercially available high-purity scandium oxide, which it is highly necessary to remove. It is currently challenging to detect trace impurities in high-purity scandium oxide, and the detection range of trace thorium and uranium is relatively high. Therefore, it is crucial to develop a technique that can accurately detect trace Th and U in high concentrations of scandium solution in the research on high-purity scandium oxide quality detection and the removal of trace impurities. This paper adopted some advantageous initiatives to develop a method for the inductively coupled plasma optical emission spectrometry (ICP-OES) determination of Th and U in high-concentration scandium solutions, such as spectral line selection, matrix influence analysis, and spiked recovery. The reliability of the method was verified. The relative standard deviations (RSD) of Th is less than 0.4%, and the RSD of U is less than 3%, indicating that this method has good stability and high precision. This method can be used for the accurate determination of trace Th and U in high Sc matrix samples, which provides an effective technical support for the preparation of high purity scandium oxide, and supports the production of high-purity scandium oxide.

Process Evaluation of Scandium Production and Its Environmental Impact

With the advancement of technology and a global shift towards clean energy, the need for rare earth metals is increasing. Scandium, a rare earth metal, has been extensively used over the decades in solid oxide fuel cells and aluminum–scandium alloys that have a vast, evolving market in aerospace, automobiles and 3D printing. However, the market struggles to maintain the supply chain due to expensive production processes and the absence of uniform global distribution of primary sources. Therefore, identification of alternative sources and technological advancements for scandium recovery are needed. To this end, an effort has been made to provide a review of the advances in different technologies applied in scandium recovery from diverse sources. Emphasis has been given to the improvements and upgrades to technologies in terms of environmental impact and recovery efficacy. An attempt has been made to discuss and deliver a clear representation of the challenges associated with every source for scandium recovery and the major developments in solving them. The environmental impact of scandium recovery and recycling has also been discussed.

Superfast preparation of Al-Sc alloys with high Sc content by spark plasma sintering

Aluminum-scandium alloys with high scandium content by mass were prepared by spark plasma sintering (SPS). The morphology, the phase composition, and the microstructures after sintering at different temperatures of Al-Sc alloy powders were investigated by scanning electron microscope (SEM), energy dispersive spectrometry (EDS), and X-ray diffractometry (XRD). The effect of sintering temperature on the microstructure of Al-Sc alloys was studied in the paper. The results show that, the Al-Sc alloy powders after ball milling are regular with the particle size of 25~45 μm, and the mechanical alloying of Al-Sc alloy powders is realized initially. In addition to the Al and Sc phases, a small amount of Al3Sc and AlSc2 are generated. The spark plasma sintering can realize the rapid densification of Al-Sc alloy with high scandium content, the Al-Sc alloy with 30% Sc by mass is successfully produced by SPS method. By adjusting the SPS process parameters, the relative density of sintered sample can be improved to 92.19%. The samples with the higher density and non-obvious grain boundary are achieved at the sintered temperature above 500℃. The second phases of Al3Sc and AlSc2 are formed by the combination of Sc with the increase of sintering temperature, and the peak intensity of Al3Sc increases gradually.

Cycle of production of aluminum-scandium alloys and alloys

Cycle of production of aluminum-scandium alloys and alloys

Study of strength properties of semi-finished products from economically alloyed high-strength aluminium-scandium alloys for application in automobile transport and shipbuilding

Abstract The results of a study on the strength of rolled products from aluminium alloys doped with scandium under various processing conditions of hot and cold rolling are presented. The regularities of metal flow and the level of strength of deformed semi-finished products from aluminum-scandium alloys are established, depending on the total degree of deformation and the various modes of single reduction during rolling. It is shown that when using one heating of a cast billet to obtain high-quality semi-finished products, the temperature during the rolling process should not be lower than 350-370°, and the total degree of deformation does not exceed 50-60%. It was found that the semi-finished products from alloys with a content of scandium in the range 0.11-0.12% in the deformed state had elevated values of ultimate tensile strength and yield strength of the metal, which allows them to be recommended for industrial production of sheet metal products.

Parallel kinetic Monte Carlo simulation of Al3Sc precipitation

The present paper reports the precipitation process of Al3Sc structures in an aluminum scandium alloy, which has been simulated with a synchronous parallel kinetic Monte Carlo (spkMC) algorithm. The spkMC implementation is based on the vacancy diffusion mechanism. To filter the raw data generated by the spkMC simulations, the density-based clustering with noise (DBSCAN) method has been employed. spkMC and DBSCAN algorithms were implemented in the C language and using MPI library. The simulations were conducted in the SeARCH cluster located at the University of Minho. The Al3Sc precipitation was successfully simulated at the atomistic scale with spkMC. DBSCAN proved to be a valuable aid to identify the precipitates by performing a cluster analysis of the simulation results. The achieved simulations results are in good agreement with those reported in the literature under sequential kinetic Monte Carlo simulations (kMC). The parallel implementation of kMC has provided a 4x speedup over the sequential version.

Aluminum-Scandium: A Material for Semiconductor Packaging

A well-known aluminum-scandium (Al-Sc) alloy, already used in lightweight sports equipment, is about to be established for use in electronic packaging. One application for Al-Sc alloy is manufacture of bonding wires. The special feature of the alloy is its ability to harden by precipitation. The new bonding wires with electrical conductivity similar to pure Al wires can be processed on common wire bonders for aluminum wedge/wedge (w/w) bonding. The wires exhibit very fine-grained microstructure. Small Al3Sc particles are the main reason for its high strength and prevent recrystallization and grain growth at higher temperatures (>150°C). After the wire-bonding process, the interface is well closed. Reliability investigations by active power cycling demonstrated considerably improved lifetime compared with pure Al heavy wires. Furthermore, the Al-Sc alloy was sputter-deposited onto silicon wafer to test it as chip metallization in copper (Cu) ball/wedge bonding technology. After deposition, the layers exhibited fine-grained columnar structure and small coherent Al3Sc particles with dimensions of a few nanometers. These particles inhibit softening processes such as Al splashing in fine wire bonding processes and increase the thickness of remnant Al under the copper balls to 85% of the initial thickness.

Influence of Substrate Bias Voltage on the Properties of Sputtered Aluminum-Scandium Thin Sheets

Thin sheets (20 μm - 30 μm) of an aluminum-scandium alloy were manufactured by magnetron sputtering with a homogeneous thickness distribution. The influence of bias voltage on the sheet properties was investigated. Steel sheets of 100 μm were employed as substrate and were coated in a dc magnetron sputtering unit fitted with a rectangular target of aluminum 2.0 w% scandium master alloy. After deposition, the substrates were dissolved in an oxidizing medium and thus freestanding aluminum-scandium thin films were obtained. The homogeneous thickness was achieved by a reciprocal movement of the substrate. The influence of a radio frequency bias voltage on the coating properties was investigated. The bias voltage resulted in an important coarsening of the columnar structure as well as an increase of the roughness and hardness. Additionally, a low bias voltage could intensively reduce the coating defect density without altering too much the sheet properties.

The characteristics of aluminum–scandium alloys processed by ECAP

Aluminum–scandium alloys were prepared having different scandium additions of 0.2, 1.0 and 2.0 wt.% and these alloys were processed by equal-channel angular pressing (ECAP) at 473 K. The results show the grain refinement of the aluminum matrix and the morphology of the Al 3Sc precipitates depends strongly on the scandium concentration. The tensile properties were evaluated after ECAP by pulling to failure at initial strain rates from 1.0 × 10 −3 to 1.0 × 10 −1 s −1. The Al–1% Sc alloy exhibited the highest tensile strength of ∼250 MPa at a strain rate of 1.0 × 10 −1 s −1. This alloy also exhibited a superior grain refinement of ∼0.4 μm after ECAP where this is attributed to a smaller initial grain size and an optimum volume fraction of dispersed Al 3Sc precipitates having both micrometer and nanometer sizes.

Strain rate and temperature effects on dynamic properties of high-strength weldable aluminum-scandium alloy

The dynamic mechanical behavior, fracture characteristics, and microstructural evolution of high-strength weldable aluminum-scandium (Al–Sc) alloy were investigated using a compressive split Hopkinson pressure bar at strain rates of 1.3 × 103, 3.6 × 103, and 5.9 × 103 s−1, respectively, and temperatures of −100, 25, and 300 °C. The results showed that the flow stress, work hardening rate, and strain rate sensitivity increase with increasing strain rate but decrease with increasing temperature. Conversely, the activation volume and activation energy increase as the temperature increases or the strain rate decreases. Moreover, the fracture strain decreases with increasing strain rate and decreasing temperature. It was shown that the Zerilli–Armstrong face-centered-cubic (fcc) constitutive equation provides accurate predictions of the mechanical response of the Al–Sc alloy under the considered strain rate and temperature conditions. Scanning electron microscopy observations revealed that the fracture surfaces of the impacted specimens are characterized by transgranular dimpled features, which are indicative of a ductile failure mode. Moreover, transmission electron microscopy observations indicated the presence of both fine and coarse randomly dispersed precipitates within the matrix and at the grain boundaries. It was found that an increasing strain rate reduces the size of the dislocation cells within the impacted Al–Sc microstructure and therefore increases the dislocation density. However, at higher temperatures, the dislocations are annihilated, leading to a reduction in the dislocation density and a corresponding increase in the dislocation cell size. The variations observed in the size and density of the dislocation cells were found to be consistent with the dynamic tendencies noted in the stress–strain response of the Al–Sc alloy.

Dynamic Deformation Behaviour and Microstructural Evolution of High-Strength Weldable Aluminum Scandium (Al-Sc) Alloy

A compressive split-Hopkinson pressure bar is used to investigate the dynamic deformation behaviour, fracture characteristics and microstructural evolution of high-strength weldable aluminum scandium (Al-Sc) alloy at strain rates ranging from 1.3 x 10 3 s -1 to 5.9 x 10 3 s -1 under room temperature conditions. The stress-strain curves reveal that the dynamic mechanical behaviour response of the Al-Sc alloy is highly sensitive to both the strain and the strain rate. As the strain rate increases, the flow stress, work hardening rate and strain rate sensitivity all increase, but the fracture strain and activation volume decrease. The Zerilli-Armstrong FCC constitutive model is applied to describe the high strain rate plastic behaviour of the Al-Sc alloy. A good agreement is found between the predicted flow response and the actual response at all values of the applied strain rate. The Al-Sc alloy specimens fracture primarily as a result of a localised shearing effect. Scanning electron microscopy observations indicate that the fracture features are characterised by a transgranular dimple-like structure. The density and depth of the dimples decrease with increasing strain rate. Transmission electron microscopy observations reveal the presence of Al 3 Sc particles in the matrix and at the grain boundaries. These particles prevent dislocation motion and therefore prompt a significant strengthening effect. The microstructural observations also reveal that the dislocation density and degree of dislocation tangling increase with increasing strain rate. The variations observed in the dislocation cell structure reflect differing degrees of strain rate sensitivity and activation volume and are found to be consistent with the observed stress-strain response of the Al-Sc alloy.

Effect of Al 3Sc precipitates on the work hardening behavior of aluminum–scandium alloys

The effect of Al 3Sc on the flow stress behavior of aluminum–scandium alloy was experimentally verified. The experimental specimens were prepared by quenching to obtain solid solution and then aged to produce Al 3Sc phase. One commercial pure aluminum specimen was included for comparison purpose. A specially designed wedge shape was rolled to obtain mechanical deformation up to 75%. Deformation mechanism was studied by the hardness technique. Upon deformation pure aluminum had shown work hardening whereas the aluminum–scandium alloy showed two distinct modes of deformation. At deformations up to 5%, dislocation motion extended across precipitates, hence strain hardening was revealed by flow stress. High deformations mode i.e. beyond 10% was completely controlled by precipitates; this is reflected by the constant value of flow stress.

Characteristics of Sputtered Al-Sc and Al-Nd Alloy Thin Films for use in Liquid Crystal Display

The interconnections among thin film transistor liquid crystal displays (TFT-LCDs) are laid on the films, made by the spotted coating method. This work studies the effect of heat-treatment, at temperatures from 523 K to 673 K, on the microstructure and physical properties of the deposited alloy thin films. The experimental results imply that, following heat treatment, the roughness of the aluminum-scandium (Al-Sc) alloy film is less than that of the aluminum-neodymium (Al-Nd) alloy, and the hillocks of the Al-Sc alloy film are lower. Accordingly, components are predicted to fail less often. The resistivity of the Al-Sc thin film is less than that of the Al-Nd thin film before it is thermally treated. Heat treatment reduces the resistivity of both, even though the reduced resistivity of Al-Nd exceeds the resistivity of the Al-Sc alloy film. Restated, the resistivity of the thermally stable Al-Sc thin film exceeds that of the Al-Nd thin film. Experimental results imply that the Al-Sc alloy is the more effective for making the driving circuit wires in the TFT-LCDs.

Resistance to Hydrogen of Al-Sc Alloys

The behavior of aluminum-scandium alloys in hydrogen at an equilibrium pressure of 0.1 MPa was studied on a Sieverts apparatus.

An Evaluation of Superplasticity in Aluminum-Scandium Alloys Processed by Equal-Channel Angular Pressing

An Al-0.2%Sc alloy and an Al-3%Mg-0.2%Sc alloy were subjected to equal-channel angular pressing to a strain of - 8 to produce grain sizes of ∼ 0.7 and 0.2 μm, respectively. Because of the presence of some areas of subgrain boundaries in the Al-3%Mg-0.2%Sc alloy, additional samples of this alloy were subjected to ECA pressing to a strain of ∼12. In both alloys, the grain sizes were reasonably stable up to annealing temperatures above 700 K. Tensile specimens were machined from the as-pressed samples for testing at elevated temperatures. The Al-3%Mg-0.2%Sc alloy pressed to a strain of ∼ 12 exhibited exceptional ductility with elongations up to a maximum of ∼ 1560% at 673 K at the high strain rate of 3.3 x 10 -2 S -1 . By contrast, the Al-0.2%Sc alloy failed under all conditions at elongations <400%. The difference in behavior between these two alloys is attributed to the nature of the deformation mechanism which serves to accommodate the superplastic process.