Sc Addition Research Articles

Effects of Sc(Zr) on the microstructure and mechanical properties of as-cast Al–Mg alloys

Both the addition of 0.6% Sc and simultaneous addition of 0.2% Sc and 0.1% Zr exerted a remarkable effect on grain refinement of as-cast Al–Mg alloys, changing typical dendritic microstructure into fine equiaxed grains. Such effect was found to be related to the formation of primary particles, which acted as heterogeneous nucleation sites for α-Al matrix during solidification. Primary particles formed in Al–Mg–Sc–Zr alloy could be identified as the eutectic structure consisting of multilayer of ‘Al3(Sc,Zr) + α-Al + Al3(Sc,Zr)’, with a ‘cellular-dendritic’ mode of growth. In addition, an attractive comprehensive property of as-cast Al–5Mg alloy due to the addition of 0.2% Sc and 0.1% Zr was obtained.

Effect of scandium on microstructure and mechanical properties of high zinc concentration aluminum alloys

This study investigated the effect of Sc addition on the microstructure and mechanical properties of a high-Zn-concentration Al (Al–49Zn) alloy. The addition of 0.5Sc obviously refined the Al grains and Zn phases in the Al–49Zn alloy during solidification. It also suppressed the Al grain coarsening and Zn dissolution in the Al–49Zn alloy during heat treatment because of the pinning effect of nanoscale Al3Sc precipitates and Sc atoms. Given its refined structure and high thermal stability, the Al–49Zn–0.5Sc alloy showed high hardness and mechanical stability after heating.

Mechanical properties of Mg-Sc binary alloys under compression

The flow stress and work hardening behaviour during uniaxial compression of dilute binary Mg-Sc alloys have been studied at 4.2K, 78K and 298K. The influences of atomic misfit, chemical misfit, solute electronic properties and stacking fault energy (SFE) on strength and ductility have been examined. The results suggest that the small atomic misfit and the reduction of SFE due to Sc additions are decisive factors in determining the mechanical behaviour of the alloys. Mg-Sc alloys deform by basal, prismatic 〈a〉, pyramidal 〈c+a〉 slip and extension twinning. Sc exerts limited strengthening on these modes due to the small atomic size and weak solute-dislocation and solute-twin boundary interactions. Constitutive modelling of the flow stress permits for the evaluation of the critical resolved shear stress (CRSS) of slip and twinning systems and determination of their activity during deformation. Analysis of activation volume and activation distance suggests that dislocation-dislocation interactions determine the flow stress. The strain rate sensitivity parameter is unaffected by alloy composition, but it decreases sharply with decreasing temperature. Mg-Sc alloys show some improvement in strength and ductility in comparison to Mg, however not as much as demonstrated by common Mg-RE binary systems. The enhancement in ductility is attributed in part to the activity of twinning and non-basal slip.

Hot Deformation and Processing Maps of Al-15%B4C Composites Containing Sc and Zr

Hot deformation behavior and processing maps of three Al-15%B4C composites denoted as the base composite (Al-15vol.%B4C), S40 (Al-15vol.%B4C-0.4wt.%Sc) and SZ40 (Al-15 vol.%B4C-0.4wt.%Sc-0.24wt.%Zr) were studied by uniaxial compression tests performed at various deformation temperatures and strain rates. The constitutive equations of the three composites were established to describe the effect of the temperature and strain rate on hot deformation behavior. Using the established constitutive equations, the predicted flow stresses on various deformation conditions agreed well with the experimental data. The peak flow stress of the composites increased with the addition of Sc and Zr, attributing to the synthetic effect of solute atoms and dynamic precipitation. The addition of Sc and Zr increased the activation energy for hot deformation of Al-B4C composites. The processing maps of the three composites were constructed to evaluate the hot workability of the composites. The safe domains with optimal deformation conditions were identified for all three composites. In the safe domains, dynamic recovery and dynamic recrystallization were involved as softening mechanisms. The addition of Sc and Zr limited the dynamic softening process, especially for dynamic recrystallization. The microstructure analysis revealed that the flow instability was attributed to the void formation, cracking and flow localization during hot deformation of the composites.

Effect of Sc and Sr on the Eutectic Si Morphology and Tensile Properties of Al-Si-Mg Alloy

To study the effect of Sc and Sr additions on modifying eutectic silicon particles and mechanical properties for Al-Si-Mg casting alloy, they were added with different amounts in F357 alloy without beryllium addition in the present work. It was found that (0.4 wt.% Sc and 0.04 wt.% Sr)-modified F357 alloy presented the optimal tensile properties when compared with the individual addition of Sc or Sr. This was mainly attributed to the synergic modification of eutectic Si in F357 alloys due to the combined additions of Sc and Sr. The silicon modification mechanisms via Sc and Sr were emphasized to be examined in this paper, and the fracture mechanism of the obtained alloys was also discussed.

Phase precipitation in transition metal-containing 354-type alloys

Abstract The present study was carried out to investigate the effects of Ni, Mn, Zr, and Sc additions, individually or in combination, on the microstructure of 354 casting alloy (Al-9 wt.% Si-1.8 wt.% Cu-0.5 wt.% Mg). Microstructural examination and thermal analysis data showed that the main reactions detected during the solidification of the six 354 alloys (G1, G6–G10) investigated are: formation of the α-Al dendritic network; precipitation of Al-Si eutectic and post-eutectic β-Al5FeSi; Mg2Si phase; transformation of the β-phase into π-Al8Mg3FeSi6 phase; and precipitation of Al2Cu and Q-Al5Mg8Cu2Si6 phases. With 2 wt.% Ni addition, the formation of Al9FeNi and Al3CuNi phases is observed. In the base 354 alloy the main phases are restricted to Cu-, Mg-, and Fe-rich intermetallic phases. The Si particle characteristics and volume fraction of intermetallics are influenced by the solidification rate and Mg level, whereas addition of Fe and/or Mn has no significant influence. In alloy G9, Fe, Mn and Ni interact to form new intermetallic phases. An increased Fe content leads to formation of polyhedral/star-like sludge particles in addition to α-Fe and β-Al5FeSi phases; the presence of the hard sludge particles within the soft α-Al dendrites improves the alloy properties.

Effect of Sc and Zr additions on microstructures and corrosion behavior of Al-Cu-Mg-Sc-Zr alloys

The effects of adding the alloy element Sc to Al alloys on strengthening, recrystallization and modification of the grain microstructure have been investigated. The combination of Sc and Zr alloying not only produces a remarkable synergistic effect of inhibition of recrystallization and refinement of grain size but also substantially reduce the amount of high-cost additional Sc. In this work, the microstructures and corrosion behavior of a new type of Al-Cu-Mg-Sc-Zr alloy with Sc/Zr ratio of 1/2 were investigated. The experimental results showed that the Sc and Zr additions to Al-Cu-Mg alloy could strongly inhibit recrystallization, refine grain size, impede the segregation of Cu element along the grain boundary and increase the spacing of grain boundary precipitates. In addition, adding Sc and Zr to Al-Cu-Mg alloy effectively restricts the corrosion mechanism conversion associated with Al2CuMg particles, which resulted in the change of the cross-section morphology of inter-granular corrosion from an undercutting to an elliptical shape. The susceptibility to inter-granular corrosion was significantly decreased with increasing Sc and Zr additions to the Al-Cu-Mg alloy. The relationships between microstructures evolution and inter-granular corrosion mechanism of Al-Cu-Mg-Sc-Zr alloys were also discussed.

The Effect of Sc Addition on Microstructure in Mg-Gd Alloys

Traditionally, Mg-Gd alloys have been strengthened by dispersed precipitates. Several reports are available about Sc addition to Mg alloys for improving a creep resistance. In this research, aging behavior of Mg-Gd, Mg-Sc and Mg-Gd-Sc alloys including the same amount of solute elements were investigated to understand the effect of Sc on microstructures and mechanical properties during aging. Hardness measurement revealed that Sc addition delayed to form precipitate. Close inspection of TEM micrographs, β” phase formed at an initial stage of aging and β’ phase was observed at a peak-aged stage in Mg-Gd and Mg-Gd-Sc alloys. In Mg-Sc alloy, there is no evidence of precipitate formation during aging at 473K.

New Progress on Er-Containing Micro-Alloying Aluminum Alloys

Erbium is an effective micro-alloying element in aluminum alloys and has been investigated intensively. Similar with the addition of Sc in aluminum alloys, nanosized L12-ordered Al3Er precipitates were formed coherently with the matrix in Er-containing micro-alloying aluminum alloys. Further, in the case of the addition of both Er and Zr, core-shell-structured Al3(ZrxEr1−x) precipitates, instead of Al3Er, were observed in a fine dispersion. Those thermally-stable precipitates can refine the grain size, minimize the segregation, homogenize the microstructure, enhance the strength, hinder the recrystallization, and thus improve the comprehensive performance of the aluminum alloys. This paper presents the effect of Er on the microstructure, mechanical properties and thermal stability of aluminum alloys. The research of some typical commercial aluminum alloys containing Er, is also reviewed here.

Precipitation of ScAl<sub>3</sub> Phase during Solutionizing and Ageing of Hypoeutectic Al-Sc Alloys and its Impact to Mechanical Properties

In this paper, precipitation of ScAl3 phase during solutionizing and ageing and its impact to mechanical properties of hypoeutectic Al-Sc alloy and effect of Sc addition amount were investigated by TEM and SEM microstructure observation and mechanical property testing. During solutionizing at 640oC for 24h, for Al-0.2wt.%Sc and Al-0.4wt.%Sc alloy, ScAl3 particles formed in the course of solidification become smaller, indicating, as a whole, Sc is partially dissolved into Al solution. Simultaneously, precipitation of two types of ScAl3 particles are observed by TEM. One has a size of 200~300nm, and the other is much small, 5~20nm in size. Though re-dissolution of Sc solute into Al solution and precipitation of large and fine ScAl3 particles occur in the solutionizing course, but the strength and hardness are decreased. The key reason for it is thought to be the softening effect of high level of vacancies in matrix lattice from the high solutionizing temperature. After further aging at 300oC for 3h, a great number of fine ScAl3 particles are precipitated in the Al matrix, which leads to a considerable precipitation hardening effect, thus the strength and hardness are increased obviously. Increasing the Sc content in the alloy results in a considerable rise in as-cast and as-aged strength and hardness, due to the solution strengthening and precipitation hardening respectively.

Effects of Sc addition on the microstructure and mechanical properties of cast Al-3Li-1.5Cu-0.15Zr alloy

Effects of Sc addition on the microstructure and mechanical properties of cast Al-3Li-1.5Cu-0.15Zr alloy were investigated by microscopy methods and tensile tests. With the addition of 0.15wt% Sc, the grain size of studied alloy in as-cast state decreased from 120µm to 30µm and did not grow obviously after two-step solution treatment (32h at 500°C+24h at 560°C). After aging at 175°C for 32h, the elongation (EL) of Sc-containing alloy reached 5.5%, which increased by 83% compared with Al-3Li-1.5Cu-0.15Zr alloy. The key factors for improvement of comprehensive mechanical properties in Al-3Li-1.5Cu-0.15Zr-0.15Sc alloy could be summarized as follows: grain refining, size reduction of δ’ phases and the precipitation of core/double-shell Al3 (Li, Sc, Zr) composite particles.

Microstructural evolution of iron-rich intermetallic compounds in scandium modified Al-7Si-0.3Mg alloys

Aluminum (Al) alloys usually have iron (Fe) as a common impurity, which has a very low solid solubility in Al and thus forms Fe-rich intermetallic compounds. Some types of Fe-rich intermetallic compounds are very harmful to mechanical properties. In this work, the microstructural evolution of the Fe-rich intermetallic compounds in scandium (Sc) modified Al-Si-Mg alloys was studied. There were two levels of Fe addition (0.2 and 0.4 wt%) and three levels of Sc addition (0, 0.2 and 0.4 wt%). Interrupted solidification experiments were performed to study the formation of intermetallic compounds. It was found that Sc reduced the nucleation temperature, minimum temperature and growth temperature of eutectic during solidification. Sc changed the morphology of Fe-rich intermetallic compounds from the α phase and β phase to Sc_3 and Sc_4 phases, and the shape of these phases was less harmful than that of the β phase. Sc changed the formation of Fe-rich intermetallic compounds from L → α-Al8Fe2Si + Al and L + α-Al8Fe2Si → β-Al5FeSi + Al into L → β-Al5FeSi + Al and L → β-Al5FeSi + Al + Si. Moreover, Sc changed the nucleation site of intermetallic compounds, causing the intermetallic compounds to solidify from the mold wall toward the mold center.

Charge compensation and electrostatic transferability in three entropy-stabilized oxides: Results from density functional theory calculations

Density functional theory calculations were carried out for three entropic rocksalt oxides, (Mg0.1Co0.1Ni0.1Cu0.1Zn0.1)O0.5, termed J14, and J14 + Li and J14 + Sc, to understand the role of charge neutrality and electronic states on their properties, and to probe whether simple expressions may exist that predict stability. The calculations predict that the average lattice constants of the ternary structures provide good approximations to that of the random structures. For J14, Bader charges are transferable between the binary, ternary, and random structures. For J14 + Sc and J14 + Li, average Bader charges in the entropic structures can be estimated from the ternary compositions. Addition of Sc to J14 reduces the majority of Cu, which show large displacements from ideal lattice sites, along with reduction of a few Co and Ni cations. Addition of Li to J14 reduces the lattice constant, consistent with experiment, and oxidizes some of Co as well as some of Ni and Cu. The Bader charges and spin-resolved density of states (DOS) for Co+3 in J14 + Li are very different from Co+2, while for Cu and Ni the Bader charges form continuous distributions and the two DOS are similar for the two oxidation states. Experimental detection of different oxidation states may therefore be challenging for Cu and Ni compared to Co. Based on these results, empirical stability parameters for these entropic oxides may be more complicated than those for non-oxide entropic solids.

Superplasticity behaviors of Al-Zn-Mg-Zr cold-rolled alloy sheet with minor Sc addition

A refined microstructure of Al-Zn-Mg-Sc-Zr alloy sheet was produced by simple hot and cold rolling to an average grain size of 3µm. Experiments were completed in electro-fluid servo-fatigue tester and results were investigated by means of optical microscope (OM), scanning electron microscopy (SEM) and transmission electron microscope (TEM). Superplastic deformation was conducted and superplastic ductility of ≥200% was achieved at a testing temperature range from 425ºC to 500ºC and relative high strain rate range of 1×10−3s−1~1×10−1s−1. The maximum elongation of 539% was obtained at 500ºC and 1×10−2s−1. In addition, the scanning electron microscopy (SEM) and transmission electron microscope (TEM) analyses showed that the presence of Al3 (Sc, Zr) particles in pinning grain boundaries and dislocations had a great influence on the superplastic deformation. The analyses of superplastic test data calculated out the coherent strain rates sensitivity parameter of 0.43 and the average activation energy of 143.762kJ/mol. The data interpreted that the dominant deformation mechanism was grain boundary sliding controlled by lattice self-diffusion.

Microstructures and properties evolution of spray-deposited Al-Zn-Mg-Cu-Zr alloys with scandium addition

In this work, the effect of Sc content on the microstructures and mechanical properties of Al-Zn-Mg-Cu-Zr alloys prepared using spray deposition was studied. Microstructure observations reveal that not only the grain size, but also the coarse secondary phase can be refined by Sc addition through the formation of a hybrid structure coupled by η-MgZn2 and Al3(Sc, Zr) phases near and at the grain boundaries. It is inferred that the primary Al3(Sc, Zr) particles can act as nucleation sites for the η-MgZn2 phase during the deposition process. With the increase of Sc content, the continuous secondary phase at the grain boundaries converts gradually into small discontinuous particles, which contributes to the considerable improvement in tensile strength and elongation. The alloy with 0.2 wt% Sc exhibits excellent combinations of ultimate tensile strength of 831±3 MPa and elongation of 10.2 ± 0.4% after T6 heat treatment, and the elongation increases by almost 50% compared to the Sc-free base alloy.

Effect of Ni, Mn, Sc, and Zr Addition on the Tensile Properties of 354-Type Alloys at Ambient Temperature

The present study was carried out to investigate the effects of Ni (high and low), Mn, Zr, and Sc additions, individually or in combination with other additives, on the microstructure and tensile properties of 354 casting alloy (Al–9 wt% Si–1.8 wt% Cu–0.5 wt% Mg) at ambient temperature following aging in the temperature range 155–300 °C for different aging times. Solution heat treatment of the studied alloys improves the tensile properties and alloy quality of all alloys. The presence of Ni and Zr (with no Cu), and Sc and Zr provides improvement as these alloys show the best YS values. Multiple aging peaks are observed in the age-hardening curves of all studied alloys, related to the precipitation sequence which occurs in each alloy. The best combination of properties is achieved after aging at 190 °C/2 h for all alloys studied, with the exception of the alloy containing 2 % Ni + 0.25 % Zr that showed the best combination at 190 °C/4 h. These conditions may therefore be considered as the appropriate T6 heat treatment parameters for these alloys. Under the experimental conditions of the present study, aging at 190 °C (for 2 or 4 h) introduces a technologically useful strategy for this particular alloy system as it provides a significant economic benefit in the form of a noticeable reduction in the aging time required to reach peak strength.

The influence of Sc solute partitioning on the microalloying effect and mechanical properties of Al-Cu alloys with minor Sc addition

A transmission electron microscope and an atom probe tomography were used to quantitatively characterize the microstructural evolution of Al-XCu alloys (X = 1.0, 1.5, and 2.5 wt%) with 0.3 wt% Sc addition. A dual solute alloying/microalloying effect on the microstructural evolution was demonstrated. On the one hand, the nucleation and coarsening of Al3Sc dispersoids displayed a Cu alloying effect. By increasing the Cu content, both the Al3Sc disperoid size and the volume fraction decreased after solution treatment. On the other hand, the precipitation of θ′-Al2Cu strengthening particles during aging treatment was promoted by Sc segregation at the θ′/matrix interfaces, showing a notable Sc microalloying effect. The strongest interfacial Sc segregation was generated in the Al-2.5 wt%Cu-Sc alloy, resulting in the most promoted θ′ precipitation. The Sc partitioning between Al3Sc dispersoids and Sc segregation at the θ′/matrix interfaces, tailored by the Cu content, impacted the mechanical properties and deformation behavior at both room temperature and high temperature. The Al-2.5 wt%Cu-Sc alloy had a room temperature yield strength of approximately 2.2 times that in its Sc-free counterpart and approximately 1.8 times that in the Al-1.5 wt%Cu-Sc alloy, which is rationalized by strengthening models. In addition, the improvement in the high-temperature mechanical properties after Sc addition was discussed in terms of the Sc segregation-induced high coarsening resistance of θ′ precipitates.

Effect of Sc addition and T6 aging treatment on the microstructure modification and mechanical properties of A356 alloy

Effect of Sc addition and T6 aging treatment on the secondary dendritic arm spacing (SDAS), modification of eutectic Si morphology, β-Al5FeSiand π-Al8Mg3Si6Fe1 phases and its effect on mechanical properties in A356 alloy has been investigated. Addition of 0.4wt%Sc in A356 alloy resulted in a 50%reduction in the secondary dendritic arm spacing (SDAS). Sc addition changed the morphology of eutectic Si from plate like to fibrous and globular. The needle like morphology of β-Al5FeSi phase in A356 alloy changed to Al5Fe(Si,Sc) phase having smaller size and irregular morphology. Transmission electron microscopy (TEM) diffraction pattern and Energy dispersive spectroscopy (EDS) analysis revealed the presence of β-Al5FeSiand π-Al8Mg3Si6Fe1 phases in A356 alloy which changed to β-Al5Fe(Si,Sc), π-Al8Mg3(Si,Sc)6Fe1 and additional V-AlSi2Sc2phase was observed in Sc containing alloys. Addition of 0.4wt%Sc to A356 alloy improved its Vickers hardness, Ultimate tensile strength (UTS), Yield strength (YS) and ductility by 20%, 25%, 20% and 30% respectively. Artificial aging treatment resulted in significant improvement in the tensile properties for both A356 and Sc added A356 alloys.

Effect of Sc and Er additions on superplastic ductilities in Al-Mg-Mn-Zr alloy

The superplasticity of Al-6Mg-0.4Mn-0.25Sc-0.12Zr and Al-6Mg-0.4Mn-0.25Er-0.12Zr (mass fraction, %) alloys sheet was investigated, and the effect of Sc and Er was discussed. The results show that the superplastic ductilities of Al-Mg-Mn-Sc-Zr alloy was higher than that of Al-Mg-Mn-Er-Zr alloy at a wide temperature range of 400-540 °C and high strain rate range of 1.67×10-4-1.67×10-1 s-1. A maximum elongation 673% is obtained at 520 °C and 1.67×10-3 s-1 in the Sc-containing alloy; while the Er-containing alloy only gets a maximum elongation 253% at 520 °C and 1.67×10-3 s-1. Moreover, the average stress exponent of Sc-containing alloy is about 2.84, which is smaller than that of Er-containing alloy (3.64). Besides, the activation energies of the Sc-containing and Er-containing alloy are 84.8 kJ/mol and 87.2 kJ/mol, respectively. It is indicated that grain boundary sliding is the dominant mechanism during tensile deformation. According to microstructure examination, the better superplasticity of Sc-containing alloy may be attributed to the presence of Al3(Sc, Zr) dispersoids, which can inhibit recrystallization and grain growth effectively.

Synergetic effects of Sc and Zr microalloying and heat treatment on mechanical properties and exfoliation corrosion behavior of Al-Mg-Mn alloys

Mechanical properties, exfoliation corrosion behavior and microstructure of Al-5.98Mg-0.47Mn and Al-6.01Mg-0.45Mn-0.25Sc-0.10Zr (wt%) alloy sheets under various homogenizing and annealing processes were investigated comparatively by tensile tests, electrochemical measurements, X-ray diffraction technique and microscopy methods. The as-cast alloys mainly consist of Fe and Mn enriched impurity phases, Mg and Mn enriched non-equilibrium aluminides and Mg3Al2 phases. During homogenization treatment, solvable intermetallics firstly precipitate and then dissolve into matrix. The optimized homogenization processes for removing micro-segregation and obtaining maximum precipitation strengthening of secondary Al3(Sc, Zr) particles are 440°C×8h and 300°C×8h, respectively. Sc and Zr additions can make the yield strength of Al-Mg-Mn alloy increase by 21MPa (6.9%), 120MPa (61.2%) and 127MPa (68.3%), when annealed at 270°C, 300°C and 330°C, respectively, indicating that Orowan precipitation strengthening caused by secondary Al3(Sc, Zr) nano-particles is much greater than grain boundary strengthening from primary Al3(Sc, Zr) micro-particles. Increasing homogenization and annealing degrees and adding Sc and Zr all can decrease corrosion current density and improve exfoliation corrosion resistance. The exfoliation corrosion behavior is dominant by anodic dissolution occurring at the interface between intermetallics and ɑ(Al) matrix. After homogenizing at 440°C for 8h and annealing at 300°C for 1h, yield strength, ultimate strength, elongation to failure and exfoliation corrosion rank are 196MPa, 360MPa, 20.2% and PA (slight pitting corrosion) in Al-Mg-Mn alloy, and reach to 316MPa, 440MPa, 17.0% and PA in Al-Mg-Mn-Sc-Zr alloy, respectively, revealing that high strength, high ductility and admirable corrosion resistance of Al-Mg-Mn alloys can be achieved by the synergetic effects of Sc and Zr microalloying and heat treatment.