Minor Sc Addition Research Articles

Study of minor Sc and Zr additions effect on silicon rich Al–Mg–Si aluminum alloy microstructure during Sc multistage thermal treatment

The study addresses the effect of multistage thermal treatment on microstructure formation of Al–Mg–Si series alloy with scandium and zirconium additions in Mg/Si = 0.3 proportion. Basic alloy AlM–Si without Sc and Zr and them modification AlMg1SiZrSc were cast. AlMgSiScZr alloy multi-stage thermal treatment included the following 4 annealing stages –550 °C 8 h + 440 °C 8 h + 500 °C 0.5 h + 180 °C 5 h. For AlMg1Si alloy it was performed following 550 °C 8 h + 180 °C 5 h practice. AlMgSiScZr microstructure was examined using scanning (SEM) and transmission (TEM) microscopy both in as-cast state and after each stage of thermal treatment, for AlMg1Si – both in as-cast state and after final thermal treatment. Coarse intermetallic particles were examined using SEM, while fine particles were examined using TEM. Besides, microhardness values were measured after various thermal treatment stages. It was found out, that coarse intermetallic compounds of Fe2Mg7Si10Al18 type are formed in both alloys during as-cast structure cooling down with such compounds partial dissolution during further thermal treatment. At the same time particles, that can be attributed either to (AlSi)3ScZr or to AlSc2Si2τ-phase, occur in inter-grain boundary of alloys with scandium-zirconium additions. No traces of scandium solid solution discontinuous decomposition have been identified during ingot cooling down. Thermal treatment during 8 h at 550 °C 8 and 8 h at 440 °C results in formation of the phase, which can represent both AlSc2Si2 and Al5SiZr2. At the same time nanoparticles (AlSi)3ScZr do not form during this thermal treatment stage. Heating to 500 °C during 30 min interval allows complete dissolution of magnesium in supersaturated aluminum solid solution. During the final stage β’’ particles (Mg5Si6), representing the major type, form in both alloys; in these conditions scandium does not produce significant effect on their formation.

Contribution of Sc doping to the growth and adhesion of alumina scale on AlCoCrFeNi high-entropy alloy

Equimolar AlCoCrFeNi high-entropy alloy (HEA) often experiences serious oxidation degradation despite its superior mechanical properties at elevated temperatures. Herein, we reveal that minor Sc addition can enhance the oxidation resistance of AlCoCrFeNi HEA at 1100 °C, and the microstructure and oxidation properties for (AlCoCrFeNi)100−xScx HEAs (Sc-0, Sc-0.1, Sc-0.5 and Sc-1) are evaluated. Except for the original A2 + B2 phases, the Laves phase is found with increasing Sc addition. Moderate Sc addition is beneficial for interface adhesion by lowering the driving force for scale spallation and enhancing the interface toughness, and excessive Sc addition, however, results in serious internal oxidation due to the generation of Sc2O3 stringers as the high diffusivity paths for inward O ions. It is also proved that enhancing the interface toughness is more beneficial to improve the oxidation resistance compared to reducing scale growth rate. Our results can offer guidance for designing advanced alloys with excellent oxidation resistance.

Achieving fully equiaxed grains with minor Sc addition of a novel Al-Li alloy fabricated by laser direct energy deposition

In this study, a novel Al-Li alloy with minor Sc addition was fabricated by laser directed energy deposition (LDED), resulting in a fully equiaxed grain structure. The precipitation behavior of primary Al3Sc particles was studied based on transient nucleation theory, and the results showed that sufficient heterogeneous nuclei by primary Al3Sc particles could preferentially form at initial solidification stage and induce into equiaxed grains. Besides, a large number of acicular T1 (Al2CuLi) phases and spherical Al3Sc phases, as well as rod-shaped TB (Al7Cu4Li) phases and quasicrystalline T2 (Al6CuLi3) phases, were distributed in as-built alloy that served as primary strengthening phases by thermal cycling. However, the specific nucleation behavior of α-Al grains on primary Al3Sc particles and subsequent growth behavior during rapid solidification need to be further investigated.

Effect of isothermal multidirectional compression on microstructure and mechanical properties of Al–Zn–Mg–Cu–Zr alloy with minor Sc addition

Sc microalloying and isothermal multidirectional compression (IMC) are important methods to refine grains and improve the mechanical properties of Al–Zn–Mg–Cu–Zr alloys. Herein, EBSD, SAXS and TEM have been carried out to investigate the effect of IMC and minor Sc on the microstructure, especially for grain boundary wetting, and mechanical properties of aged Al–Zn–Mg–Cu–Zr alloys by melting and hot compression process parameter optimization. The results show that the strength and plasticity can be obviously improved simultaneously by minor Sc addition and IMC. Especially, stripy GBs (one kind of typical GB complexion) have been widely observed for alloy samples after microalloying Sc and IMC, which indicates the occurrence of GB wetting for Al–Zn–Mg–Cu–Zr alloy. And the GB wetting degree gradually increases for alloys with only microalloying Sc, only IMC and (microalloying Sc + IMC). Combined with GB wetting, the formation of Al3(Sc, Zr) due to Sc addition could inhibit the motion of dislocation and grain boundary, which promotes formation and inhibit growth of recrystallized grains, leading to further grain refinement. Besides, GB wetting degree would affect the precipitate distribution, especially for grain boundary precipitates. Also, GB wetting probably promote grain bridging, which is beneficial to improve the yield strength and ductility of Al–Zn–Mg–Cu–Zr alloys. The concurrent effect of grain refinement, the precipitate including finer Al3(Sc, Zr) particles, dislocation strengthening and grain bridging contribute to the simultaneous improvement of the strength and ductility of Al–Zn–Mg–Cu–Zr alloys under IMC and Sc. This study provides a new understanding on microalloying Sc combined with IMC on the microstructure and properties of Al–Zn–Mg–Cu–Zr alloys.

The microstructural features and strain recovery characteristics of Ti–V–Al shape memory alloy with minor Sc addition

In the present work, minor Sc addition was employed to control the microstructural features, further optimizing the mechanical/functional performances of Ti–V–Al based shape memory alloy. The results revealed that phase constituents of Ti–V–Al based shape memory alloys were dominated by single αˊˊ martensite phase, regardless of Sc content. Nevertheless, Sc addition caused the significant lattice distortion of Ti–V–Al based shape memory alloy. Meanwhile, the grain size of Ti–V–Al based shape memory alloys were reduced due to Sc addition. Besides, the martensite morphologies evolved from self-accommodation configuration to optimal orientation configuration, but the types of twins kept unchanged. All Ti–V–Al based shape memory alloys showed the reversible αˊˊ→β martensitic transformation in heating curves, irrespective of Sc content. With Sc content increasing, the martensitic transformation temperatures increased linearly due to the chemical composition effect and mechanical effect. Moderate Sc addition was favor to the improvement of thermal cycling stability of Ti–V–Al based shape memory alloys, which can enhance its functional stability. In proportion, the mechanical and functional properties of Ti–V–Al based shape memory alloys firstly increased and then decreased. Ti–V–Al based shape memory alloy with moderate Sc content of 0.025 at.% possess the higher fracture strength of 748.4 MPa, superior ductility of 18.7% and the larger shape memory effect strain of 4.31% under the 8% pre-strain condition. The higher performances in Ti–V–Al shape memory alloy with 0.025 at.% Sc can be attributed to the compressive effect of solution strengthening and grain refinement.

Enhancing the creep resistance of a cast AZ91 alloy via minor Sc addition

The influence of 0.2 wt% Sc addition on the microstructure and creep characteristics of a cast AZ91 magnesium alloy was studied by impression creep tests under the constant punch stresses ranging from 175 to 700 MPa in the temperature range 425–525 K. The findings indicated that creep rates decreased at all stress levels and temperatures after Sc addition. This was ascribed to the formation of the thermally stable Al3Sc and Mg5Al4Sc particles, reduction in the quantity of the unstable β-Mg17Al12 phase, and solid solution strengthening of Al in the Mg matrix. The creep stress exponent and activation energy values obtained from the studied alloys ranged from 5–6 and 95–117 kJ/mol, respectively. The detected drop in creep activation energy with increasing stress implies that two concurrent mechanisms of dislocation climb controlled by lattice and pipe-diffusion are competing with each other. The former one was the governing mechanism at low stress levels, while the latter one was the prevailing mechanism in the high stress regimes.

The mechanisms of the high-strain-rate superplastic deformation of Al-Mg-based alloy

High-performance aluminum-based alloys exhibiting a high-strain-rate superplasticity improve the formability of lightweight constructions with complex shapes. The microstructural evolution and contributions of the deformation mechanisms to the total strain during high-strain-rate superplastic deformation of Al-Mg-based alloy with minor Sc and Zr additions were analyzed. Strain-induced changes in the grain/subgrain structure confirmed the dynamic recrystallization even at large strains. The evolution of the surface structure with focus ion beam milled grids confirmed that grain boundary sliding provided up to 40% of the total strain. The role of dislocation slip/creep increased and diffusional creep decreased with an increase in the strain rate.

Effect of Sc and Zr on microstructure and chemical milling surface roughness of 2024-T6 alloy sheets

Chemical milling is one of the most widely used processing methods for Al alloys in the aerospace and aircraft industries. The surface roughness significantly impacts the mechanical performance of chemically-milled products. Therefore, it is rational to develop a strategy to control the surface roughness. In this study, the effect of minor Sc and Zr additions on the microstructure and chemical milling surface roughness of a 2024-T6 alloy sheet was investigated. The additions optimized the surface roughness, and values of (0.7377 ± 0.0024) and (0.9053 ± 0.0018) μm in the rolling and transverse directions respectively, were achieved, which were significantly lower than those achieved by the 2024 alloy ((1.0785 ± 0.0026) and (1.2205 ± 0.0021) μm, respectively). The 2024SZ (2024-0.1Sc-0.2Zr Al) alloy exhibited fine and discontinuous grain boundary intermetallic particles (IMPs) in the as-cast state. Thermo-Calc software showed that the 2024 SZ alloy formed L12-Al3(Sc, Zr) phases during solidification, which induced heterogeneous nucleation and refined the grains. The weight fraction of IMPs in the 2024SZ alloy was much considerably smaller than that in the 2024 alloy during solidification. These IMPs affected the density of the IMPs in the T6 state. Finally, the mechanism of Sc and Zr on the chemical milling surface roughness of the 2024-T6 alloy was demonstrated. This study provides a feasible strategy for optimizing the chemically-milled surface roughness of Al alloys.

Effect of minor Sc additions on precipitation and mechanical properties of a new Al-Cu-Li alloy under T8 temper

The effects of minor Sc additions on the formation of various precipitates and mechanical properties of a new Al-Cu-Li alloy have been experimentally investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), three dimensional atomic probe (3DAP) analysis and tensile tests. Under T8 temper, the introduction of 0.092 wt% Sc accelerates the aging response of Al-Cu-Li alloy and induces a little reduction in the tensile and yield strength due to the decrease of solid solubility of Cu in Al alloy matrix and number density of T1 (Al2CuTi) strengthening phase, which are closely linked with the formation of insoluble Sc-containing W(AlCuSc) phase by consuming Cu solutes for the precipitation of T1 phase. Except for T1 and W phase, Nanoscale Al3(Sc,Zr) and S′ phases are also found after minor Sc addition. The 3DAP tomography indicates that the Al3(Sc,Zr) precipitates have a core-shell structure with Zr atoms mainly close to the shell and Sc atoms enriched in the core. It is believed that such precipitate is only probably composed of Al and Sc at the initial stage, and then Zr enters into them at the later stage, which hinders the diffusion of Sc in the matrix through the boundary into the interior of the particle and thus makes the coarsening rate of Al3Sc decrease.

Effect of minor Sc addition on high temperature tensile behavior of Al–7Zn–2Mg–2Cu–0.2Zr alloy

Alloys of Al–7Zn–2Mg–2Cu–0.2Zr and Al–7Zn–2Mg–2Cu–0.2Zr–0.2Sc were prepared by extrusion casting. Elongation–to–failure tests and strain–rate–change tensile tests were conducted at 300, 350, 400 and 450 °C, and deformation mechanisms were investigated based on microstructure, stress exponent and deformation activation energy. The results show that the 0.2 wt% Sc addition improves both tensile ductility and strength by refining grains and forming second phase particles. Primary Al3(Sc, Zr) particles precipitate during solidification and refine the as–cast grains, and secondary Al3(Sc, Zr) particles precipitate and interact with moving dislocations during high temperature deformation. The Sc addition has no significant effect on high temperature deformation mechanism. The deformation of both alloys is dominated by dislocation creep strengthened by second phase particles at 300 and 350 °C. Such strengthening effect weakens with the increase in temperature, and the deformation transfers to solute–drag dislocation creep at 450 °C.

Effect of Minor Sc Addition on Microstructure and Tensile Properties of Hot-Extruded 7055 Alloy

Effect of Minor Sc Addition on Microstructure and Tensile Properties of Hot-Extruded 7055 Alloy

Effects of Sc on the microstructure and properties of in situ ZrB2/7085Al composites

The microstructure and mechanical properties of the ZrB2/7085Al composites containing Sc were studied. The ZrB2/7085Al composites were prepared by in situ reaction via Al-Zr-B system. On addition of Sc, it interacted with Zr present in the alloy resulting in the production of Al3(Sc, Zr) precipitates. Minor addition of Sc resulted in grain refinement, change in ZrB2 nanoparticles distribution, change in the size and morphology of the η phase and formation of Al3Sc and Al3(Sc, Zr) precipitates, which improved the strength significantly. The ultimate tensile strength (UTS), yield strength (YS) and elongation of 7085Al-ZrB2-Sc increased to 660.2, 603.4 MPa and 10.6%, respectively. These tensile properties improved 20.4%, 19.2% and 73.7%, respectively, over the 7085Al.

Effect of Minor Sc Addition on the Microstructure Evolution of Al–Cu–Li–Mg Alloy During Homogenization with Different Cooling Modes

Effect of Minor Sc Addition on the Microstructure Evolution of Al–Cu–Li–Mg Alloy During Homogenization with Different Cooling Modes

Influence of minor Sc additions on grain refinement and microstructure characteristics of a high Zn-containing Al-Zn-Mg-Cu-Zr alloy

Influence of minor Sc additions on grain refinement and microstructure characteristics of a high Zn-containing Al-Zn-Mg-Cu-Zr alloy

The influence of Sc and Zr additions on microstructure and corrosion behavior of AA5182 alloy sheet

Minor additions of Sc and Zr to a 5182 base alloy were used to study the effects of microstructure on the susceptibility to intergranular corrosion (IGC) of 5xxx sheet alloys. The results showed that minor Sc and Zr additions significantly decrease the IGC susceptibility as measured by the depth of IGC for the high-temperature annealed sheet. The improvement in IGC resistance is attributed to a high number density of nano-scaled coherent Al3(Sc,Zr) dispersoids which resist recrystallization, and produce a fine subgrain structure. The character of the subgrain structure is critical to prevent the occurrence of continuous intergranular Al3Mg2 precipitates during sensitization.

Role of Minor Sc Addition on Precipitation and Mechanical Properties of a New Al-Cu-Li Alloy Under T8 Temper

Role of Minor Sc Addition on Precipitation and Mechanical Properties of a New Al-Cu-Li Alloy Under T8 Temper

An as-cast Nb-Si-based alloy with fine-grains and remarkable fracture toughness by minor Sc addition

The effect of Sc addition on the phase composition, microstructure, and room-temperature fracture properties of arc melted Nb-Si-Ti-ZrC-based alloys was systematically investigated. The constituent phases of all alloys are Nbss, γ-(Nb,X)5Si3 and TiC. Sc refines the microstructure, while the grain sizes for the primary γ-(Nb,X)5Si3 and Nbss phases drop from 213 µm and 22.3–23 µm and 5.7 µm, respectively. The content of Nbss and TiC decreases with increasing Sc. The Sc dissolves and then softens Nbss phase. The degree of restraint of Nbss phase decreases with increasing Sc content, therefore causing formation of dimples in the fracture and interface decohesion. Because of the refinement of the primary γ-Nb5Si3 phase, the dimples and interface decohesion created by the low degree of constraint of Nbss phase, the KQ value of Sc3 alloy becomes 16.4 MPa·m1/2. The average grain size of Nbss phase becomes the lowest (5.7 µm), when 0.5 at% Sc is added. The small grain size of Nbss phase deteriorates room-temperature fracture toughness.

Hydrogen activation and storage properties of laves phase Ti1-xScxMn1.6V0.4 alloys

Hydrogen activation, storage properties and associated crystal structures of Ti1-xScxMn1.6V0.4 (x = 0, 0.05, 0.1, 0.15, 0.2, 0.25) alloys are investigated by hydrogenation and XRD. The unit-cells of alloys and hydrides expand with Sc content and hydrogen concentration. Minor addition of Sc significantly improves hydrogen activation and storage properties. The plateau pressure decreases, whereas the sloping factor and relative partial molar enthalpy for hydrogenation increase with Sc content. The activation properties strongly depend on the particle sizes. The bulk samples can easily be activated by implementing a hydrogen-induced cracking mechanism, which avoids removal of protective oxide films and compensates the lack of metallic B-metal in catalysis of hydrogen dissociation. Samples with smaller particle sizes are difficult to activate. The unusual particle size effect is interpreted by activation kinetics, and attributed to the high oxygen binding ability of B-metals and their contribution to the surface oxide films.

Effect of Minor Sc and Zr Addition on the Microstructure of 7075 Aluminum Alloy during Homogenization Treatment Process

Effect of Minor Sc and Zr Addition on the Microstructure of 7075 Aluminum Alloy during Homogenization Treatment Process

Microstructure evolution and microhardness of the novel Al–Cu–Li-xSc alloys fabricated by laser rapid melting

Al–Li alloys containing scandium serve as excellent lightweight materials. However, the number of Al3Sc phases is extremely less due to the minor addition of Sc, resulting in deficient microhardness. Laser rapid melting has the advantage of enhancing solid solubility of alloying elements during rapid solidification, which becomes a critical technique to explore new components of alloys. This study aims to investigate the effects of major Sc content (0, 1, 3 and 5 wt%) on microstructure and microhardness of Al–Cu–Li-xSc alloys fabricated by laser rapid melting. The primary Al3Sc particles could greatly refine grains in Al–Cu–Li-1Sc alloy. With the increase of Sc content, more clustered Al3Sc particles nucleated during the latter stage of solidification but the grain refinement effect was not obvious. The growth restriction factor (Q) was calculated to determine the degree of constitutional supercooling (ΔTCS) that served as segregation of Sc during solidification. The spiculate T1 (Al2CuLi) precipitates heterogeneously nucleated on the Al3Sc dispersoids. The maximum value of microhardness is 167 HV obtained in aged Al–Cu–Li-5Sc alloys. The novel Al–Cu–Li-xSc alloys can be designed as gradient hard Al–Li alloy materials.