Sc Addition Research Articles

New Twin-Roll Cast Al-Li Based Alloys for High-Strength Applications

Al-Li based alloys are attractive materials for the aerospace industry. The twin-roll casting of such materials could provide properties not achievable by conventional direct-chill casting and downstream processing methods due to significantly higher solidification rates. An Al-Li-Cu-Mg-Zr alloy was twin-roll cast with the same alloy containing a small addition of Sc. The microstructure of as-cast materials and the influence of Sc on the behavior of the alloy at elevated temperatures were studied by means of light and electron microscopy and by resistivity measurements. A fine-grained structure was formed during twin-roll casting, but several surface and internal defects were found on the strips, which should be suppressed by a further adjustment of the casting conditions. The addition of Sc had a positive effect on grain size uniformity and microstructure stabilization at elevated temperatures, as shown by the precipitation of a fine dispersion of coherent Sc- and Zr-containing precipitates.

The microstructure and weldability in welded joints for AA 5356 aluminum alloy after adding modified trace amounts of Sc and Zr

Abstract Different AA5356 alloy filler metals containing various amounts of Sc and Zr are obtained and applied to join the 5083 aluminium plate with 2.8 mm thickness. A significant grain refinement can be observed in the fusion zone (FZ) of welded joints after the additions of Sc and Zr. The filler metal modified with 0.2 wt.% Zr+0.1 wt.% Sc obtained the smallest grain size with 29 μm, and the filler metal with 0.2 wt.% Sc+0.1 wt.% Zr additions got the similar grain size with 30 μm. The 0.2 wt.% Sc addition can effectively modify the microstructure of filler metal and improve the mechanical properties. The grain size of fusion zone for AA5356 + 0.2 wt.% Sc+0.1 wt.% Zr filler metal decreased by 75.8 % and the highest ultimate tensile strength (UTS) increases by 15 % compared with the unmodified alloy joints. However, individual 0.2 wt.% Zr addition cannot effectively modify the filler metal. The improvement of mechanical properties can attribute to the presence of refined grains.

Effect of Al3(Sc,Zr) dispersoids on the hot deformation behaviour of 6xxx-series alloys: A physically based constitutive model

The hot deformation behaviour of two model Al–Mg–Si alloys was assessed. One alloy was representative of the 6xxx series containing small additions of Mn and Cr, while the other contained small additions of Sc and Zr. Prior to deformation, a multi-stage heat treatment was conducted on the alloys to solutionize the Mg and Si and promote the precipitation of Al3(Sc,Zr) dispersoids in the Al–Mg–Si-Sc-Zr alloy. Uniaxial hot compression tests were conducted at various temperatures (683–823 K) and strain rates (1–125 s−1) and the resulting flow stress-strain curves were evaluated. Flow stress values were observed to be slightly increased in the alloy containing Sc and Zr. The activation energy for hot deformation and material constants for each alloy were calculated, which in turn provided a good prediction of the experimental data. The post-deformation microstructures were analysed using SEM and TEM. The capacity for dynamic recovery was reduced, while dynamic recrystallization was prevented in the Al–Mg–Si-Sc-Zr alloy. This was a result of restricted dislocation motion, caused by the pinning of dislocations from the Al3(Sc,Zr) dispersoids. The relative flow stress of the Al–Mg–Si-Sc-Zr alloy was found to compare favourably to other 6xxx series alloys with similar mechanical properties.

Effects of rare earth elements on the microstructure and wear properties of TiB2 reinforced aluminum matrix composite coatings: Experiments and first principles calculations

In this work, effects of rare earth elements on microstructure evolution and wear properties of TiB2 reinforced aluminum matrix composite coatings were investigated by the combination of first principles calculations and experimental investigation. The calculated results revealed that Sc exhibited the most effective modification ability due to the most negative adsorption energy and the largest charge transfer compared with La and Y. Based on the calculated results, the rare earth elements modified composite coatings were synthesized by laser processing. The as-obtained composites were characterized by back-scattered electron imaging (BSE) and spherical aberration corrected scanning transmission electron microscopy (Cs-corrected STEM). Results indicated that the addition of Sc can greatly refine the particle size of TiB2, improve the distribution of particles and lead to the morphology transforming from hexagonal disk to sphere. As a result, the microhardness and wear properties of the composite coatings were enhanced significantly. The best properties were achieved in the composite with 0.6 wt% Sc addition, which exhibited highest microhardness of 920 HV, lowest friction coefficient of 0.4 and wear rate of 24.8 mg /h. The preferential adsorption of rare earth elements on TiB2 facets is proposed to be the main modification mechanism which results in the morphology evolution and wear properties improvement.

Effects of Sc addition and aging on microstructure and martensitic transformation of Ni-rich NiTiHfSc high temperature shape memory alloys

In this study, the effects of Sc addition and aging on the microstructure and martensitic transformation of Ni50.3Ti29.7-xHf20Scx(x = 0, 0.5, 1, and 2 at.%) alloys were investigated. The addition of Sc resulted in the formation of Sc2O3 phase along with the martensite and (Ti,Hf)4Ni2Ox at room temperature. The Ni content of the matrix increased slightly with an increase in the Sc content up to 1 at.% and then decreased with a further increase in the Sc content to 2 at.%. The transformation temperature of the solution-treated NiTiHfSc alloys first increased at a rate of 52 °C/1 at.% Sc and then decreased at a rate of 42 °C/1 at.% Sc. The effect of aging at 550 °C for 3 h on the precipitation of the H-phase in the alloys depended on their Sc content. With an increase in the Sc content, the volume fraction of the H-phase first decreased and then increased attributing to the Ni content in the matrix and the evolution of the secondary phase. After aging, the characteristic temperatures of martensitic transformation were elevated as compared to those of solution-treated alloys because of the precipitation of the H-phase. With an increase in the Sc content up to 1 at.%, the increment in transformation temperature was first reduced and then increased with further increasing Sc content to 2 at.%. This can be attributed to the change in the H-phase volume fraction with the Sc content.

Electron beam welding behavior of a 5083-H15 alloy containing Zr and Sc

This study discusses the effects of the addition of Sc and Zr on the microstructure, and mechanical and corrosion properties of an electron beam welded 5083-H15 alloy. The results show that the addition of Sc and Zr to a 5083 alloy exerted a remarkable effect on grain refinement resulting in an enhancement of the mechanical properties. Moreover, the addition of Sc and Zr prompted precipitation of Al3 (Sc, Zr) precipitate in the heat-affected zone during the electron beam welding, thereby hindering the movement of dislocations and inhibiting recrystallization, effectively improving the tensile strength, joint efficiency, and hardness of the welded joint. Combined additions of Sc and Zr to a 5083 alloy led to a remarkable enhancement in the resistance to intergranular corrosion at the weld joints as determined via nitric acid mass loss tests for a reduction from 9.72 to 3.61 mg/cm2. The main reason for the improvement in corrosion resistance is the addition of Sc and Zr. Recrystallization at the welded joint was inhibited by the formation of the Al3 (Sc, Zr) phase during the electron beam welding which acted to suppress the formation of the β phase along the grain boundaries in the welded zone.

Effect of Sc Addition on Magnetic and Optical Properties of YFeO₃ Nano Particles

Multiferroic Sc-doped YFeO₃ nanoparticles were obtained by a low-temperature solid-state reaction route. It indicated that with the addition of Sc, nanosized YFeO₃ powders were obtained at 800 ℃, and the orthorhombic phase was transformed into the hexagonal structure. Magnetic hysteresis loop illustrated the magnetic property of YFeO₃ nanoparticles improved with Sc doping. The maximum magnetization of the powders was about 4.00 emu/g, showing that the energy gap can be reduced to 2.25 eV and thus the doping nanoparticles can be used in optical field. Therefore, the optical and magnetic properties of the material can be obviously enhanced with Sc doping, proving its potential application in magnetic and optical fields.

Microstructure and corrosion behavior of Mg-Sc binary alloys in 3.5 wt.% NaCl solution

This paper studied the microstructure and corrosion behavior of Mg-xSc binary alloy (x = 0.1–1.5 wt.%) sheets. Sc has a significant effect of refining grains of Mg. The Mg-Sc binary alloys had a single-phase microstructure for Sc concentrations between 0.1−0.3 wt.%, while there were Mg-Sc precipitates for higher Sc concentrations. The Sc additions obviously improved the corrosion resistance of pure Mg due to the refinement of microstructure and the formation of a more protective corrosion products film. The corrosion rate firstly decreased and then increased with increasing Sc concentration. Mg-0.3Sc has the lowest corrosion rate.

Effect of Sc Content on the Microstructure and Properties of Al–Mg–Sc Alloys Deposited by Wire Arc Additive Manufacturing

Despite showing considerable potential, wire arc additive manufacturing (WAAM) has been limited to producing Al–Mg alloys. As the addition of Sc can improve the mechanical properties of Al–Mg alloys, in this study, Al–Mg–Sc alloy deposits with different Sc contents were prepared by a WAAM process. The porosity, microstructure, and mechanical properties of the deposits were studied. At Sc contents less than 0.15%, Sc was completely dissolved in the Al matrix without grain refinement, and the mechanical properties were slightly improved. At a Sc content of 0.3%, the primary Al3Sc phase precipitated out of the as-deposited body, resulting in an abrupt change in the microstructure, significant grain refinement, significantly increased tensile strength and yield strength, with a tensile strength, yield strength, and elongation of 372 MPa, 270 MPa, and 22.5%, respectively. Following heat treatment at 350 °C for 1 h, the grain boundaries were refined and the secondary Al3Sc phase was precipitated. Furthermore, the tensile strength and yield strength were significantly increased to 415 MPa and 279 MPa, respectively, and elongation decreased to 18.5%. At a Sc content of 0.45%, due to the aggregated precipitated phase, the coarsened grain boundaries and the limited solid solution amount of Sc in the α(Al) matrix (~ 0.25%), the mechanical properties were not further improved compared with the deposit with Sc content of 0.3%. Thus, based on economic considerations, the optimal Sc content was 0.3%. Owing to their enhanced mechanical properties, WAAM-produced Al–Mg–Sc alloys are expected to have a wide range of applications in aviation, aerospace.

Improved wear resistance of biodegradable Mg–1.5Zn–0.6Zr alloy by Sc addition

Magnesium alloys exhibit significant potential for use in next-generation biodegradable materials. Implanted magnesium alloys are expected to exhibit good wear resistance. In this work, the effects of rare earth metal Sc on the wear resistance of biodegradable magnesium alloys were studied. The average grain sizes of Mg–1.5Zn–0.6Zr–xSc (ZK21–xSc, x = 0, 0.2, 0.5, 1.0; wt%) alloys decreased with Sc content increasing. Unlike other rare earth metals, the grain refinement mechanism of Sc belongs to the heterogeneous nucleation mechanism. The yield tensile strengths and Vickers hardness of the ZK21–xSc alloys markedly improved with the addition of Sc increasing. This could be due to the grain refinement and enhanced bond energy resulting from Sc addition. Moreover, the friction and wear tests showed that the friction coefficient of the alloys decreased and the weight loss reduced with Sc addition increasing. This implies that Sc addition could enhance the wear resistance of magnesium alloys. With the addition of Sc increasing, the peeling phenomenon weakened gradually and the worn surfaces of samples became smoother. The major wear mechanisms of the as-cast ZK21–xSc alloys were abrasion wear and delamination wear.

Phase transformations in commercial cold-rolled Al–Zn–Mg–Cu alloys with Sc and Zr addition

The influence of cold rolling on thermal and mechanical properties together with microstructure observation of cast AlZnMgCu(ScZr) alloys has been investigated. Differential scanning calorimetry measurements and microhardness were compared to microstructure that was observed by microscopy (scanning electron and transmission), electron backscatter and X-ray diffractions. Microstructure observation of all studied alloys proved eutectic phase at (sub)grain boundaries. The eutectic phase at grain boundary in the AlZnMgCuScZr has a disordered quasicrystalline structure (known as the T phase or Mg32(Al,Cu,Zn)49). In the AlZnMgCu alloy, the eutectic phase consists of two phases—predominant MgZn2 phase and minor quasicrystalline T phase. During casting and subsequent cooling, multilayer primary Al3(Sc,Zr) particles also precipitated in the alloy with Sc,Zr addition. Solute clusters and/or Guinier–Preston zones were dissolved during the annealing up to ~ 170 °C in the alloys. The highest hardening is caused by particle formation of metastable η′ and stable η phase in AlZnMgCu system observed at ~ 200 °C. Precipitation of the secondary Al3(Sc,Zr) particles is probably the reason of hardening after annealing above 300 °C in the Sc,Zr-containing alloys. Melting of eutectic phases was observed in DSC curves at temperatures ~ 481 and ~ 493 °C in the studied alloys. Activation energies of the Guinier–Preston zones dissolution and/or solute clusters were calculated using Kissinger and Starink method as QA ≈ 100 kJ mol−1 and the formation of the particles of Al–Zn–Mg–Cu system as QB ≈ 150 kJ mol−1. No significant effect on the calculation of activation energy values of thermal processes was observed in deformed alloys. Sc,Zr addition in the alloys stabilizes grains, and there is no recrystallization in the AlZnMgCuScZr alloy at temperature 450 °C/10 h.

Effects of minor Sc and Zr additions on mechanical properties and microstructure evolution of Al−Zn−Mg−Cu alloys

Abstract The effects of minor Sc and Zr additions on the mechanical properties and microstructure evolution of Al−Zn−Mg−Cu alloys were studied using tensile tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ultimate tensile strength of the peak-aged Al−Zn−Mg−Cu alloy is improved by about 105 MPa with the addition of 0.10% Zr. An increase of about 133 MPa is observed with the joint addition of 0.07% Sc and 0.07% Zr. For the alloys modified with the minor addition of Sc and Zr (0.14%), the main strengthening mechanisms of minor addition of Sc and Zr are fine-grain strengthening, sub-structure strengthening and the Orowan strengthening mechanism produced by the Al3(Sc,Zr) and Al3Zr dispersoids. The volume of Al3Zr particles is less than that of Al3(Sc,Zr) particles, but the distribution of Al3(Sc,Zr) particles is more dispersed throughout the matrix leading to pinning the dislocations motion and restraining the recrystallization more effectively.

Understanding grain refinement of Sc addition in a Zr containing Al-Zn-Mg-Cu aluminum alloy from experiments and first-principles

In this work, we present a better insight into the grain refining mechanism of Sc addition in an Al-Zn-Mg-Cu-Zr aluminum alloy from experiments and first-principles. It is found a higher concentration of Sc can result in finer grains, but the refining efficiency was sharply decreased when the Sc/Zr ratio(wt.%) exceeds 1. Also, we determined the L12-Al3(Sc, Zr) was formed by Sc displacing Zr in L12-Al3Zr, and those generated particles distributed around L12-Al3Zr. Moreover, the content of Zr was found overwhelmed by Sc within a Sc and Zr containing particle in high Sc/Zr ratio alloys. The calculated surface energy indicates a low Sc doping (<21.4 at.%) tends to stabilize L12-Al3Zr(111) surface, when the doping content in the range of 21.4–35.7%, the clean L12-Al3Zr(111) is energetically favored, when the doping content is higher than 35.7%, the L12-Al3(Sc, Zr)(111) is preferred. Based on the interface energy, the capability of heterogeneous nucleation to α-Al can be ordered as L12-Al3(Sc, Zr) > L12-Al3Zr > L12-Al3Sc. However, in a Sc rich condition, the formation of L12-Al3(Sc, Zr)(111) and Al(111)/L12-Al3(Sc, Zr)(111) interface were hindered by the formation of L12-Al3Sc(111), thus, further refinement of grains was limited, the results well explained the experimental observations.

Effects of scandium and silicon addition on the microstructure and mechanical properties of Ti-6Al-4V alloy

Titanium alloys are excellent candidates for structural components submitted to high temperature owing to their high strength to weight ratio, good corrosion resistance and metallurgical stability. Due to the complex service conditions of spacecraft, the creep property of titanium alloy has been recognized. The microstructural evolution, mechanical properties of Ti-6Al-4V-xSi-ySc alloys have been investigated. Alloys were prepared by three times vacuum arc remelting followed forging, rolling and heat treatment at 950°C/0.5h/AC and 510°C/5h/AC. Then specimens were subjected to uniaxial tensile and creep test. The strengthening and creep resistance mechanism of the alloys were analyzed. The results shown that the grain sizes of alloys were refined significantly by Sc and Si addition. The Si and Sc plays a role in grain refinement and solid solution strengthening. At the same time, the alloy matrix was purified due to the formation of Sc2O3 particles. The Si and Sc addition improve the creep resistance comparing the base alloy. This can be attributed to the strengthening of solid solution of Si and the silicide also have the inhibiting effect on the dislocation movement during creep. Si promote the diffusion of V and suppress the formation of α2 phase. Sc in titanium alloy has three forms, some of which are solid-dissolved, some of which form Sc2O3, and some of which form horseshoe-shaped Al3Sc. The formation of Al3Sc particles is helpful to improve the creep properties of titanium alloy. Sc can inhibit the precipitation of silicide and promote the formation of α2 phase, which are helpful to improve the creep resistance of titanium alloy.

Preparation and oxidation behaviour of NiCrAlYSc coatings on a Ni-based single crystal superalloy

The NiCrAlYSc coatings with different Sc content were prepared on the Ni-based superalloy by arc ion plating. Cyclic and isothermal oxidation behaviours of all the coatings were investigated. The results show that an appropriate addition of Sc in the coating can significantly improve the scale adhesion, shorten the transient oxidation stage and promote the transformation from θ-Al2O3 to α-Al2O3. The effects of Sc addition on the oxidation performance of the coating as well as the mechanism of oxide adherence were discussed.

Mechanical properties of defective L12-Al3X (X = Sc, Lu) phase: A first-principles study

The mechanical properties of Al3X (X = Sc, Lu) were studied by density functional theory (DFT). The elastic constants and formation enthalpy indicate that the L12-Al3X (X = Sc and Lu) are mechanically and thermodynamically stable. The bulk moduli and shear moduli show that Al3Sc has better resistance to volume and shape changes than Al3Lu. However, the calculated results show that Al3Lu has better plasticity than Al3Sc. The properties of structural stability and elastic moduli of the crystal containing four major types of point defects in L12-A13X (X = Sc and Lu) were calculated. The mechanical properties of point defects show that point defects cause L12-Al3X lattice distortion and change the corresponding elastic constants. Point defects reduce the Young's, shear and bulk moduli but have little effects on the crystal brittleness and toughness of Al3Sc and Al3Lu. Therefore, we have found that Lu addition into aluminum alloys is a very good replacement for expensive Sc addition when the L12 structures are desired for nucleation or strengthening precipitates in aluminum alloys.

Effect of scandium addition on microstructure and mechanical properties of as-cast Al-5%Cu alloys

Grain refinement is one of the effective methods to improve the yield strength and toughness of Al-Cu alloys. The effects of Sc addition (0.2%, 0.4%, 0.6%, 0.8% and 1.0 wt%) on the microstructural evolution and mechanical properties of as-cast Al-5%Cu alloys were studied. The as-cast samples were characterized by optical microscope (OM), transmission electron microscopy (TEM), scanning electron microscope (SEM) and electron probe microanalysis (EPMA). The results revealed the primary α-Al occurred to obvious change from developed dendrites to fine equiaxed grains with the increasing Sc content in Al-5%Cu alloy. When the addition concentration of Sc reaches 0.8%, the developed α-Al dendrites were significantly refined and the average size of α-Al decreased from 218.3 μm to 29.6 μm. Moreover, the morphology and size of θ-Al2Cu phases of Al-5%Cu alloy caused noticeable changes with the increase of Sc concentration. Mechanical properties test illustrated that the ultimate tensile strength (UTS), yield strength (YS) and elongation (El) increased by 61.59%, 66.82% and 57.20%, respectively, which could be attributed to microstructure refinement and fine Al3Sc particle precipitate.

Effect of microalloying and tensile deformation on the internal structures of eutectic Si phase in Al-Si alloy

The microstructure and tensile property of the hypoeutectic Al-Si alloy with and without microalloying of Sc and Zr were studied by means of the optical microscope (OM), Transmission electron microscopy (TEM) and the tensile test. The focus of this work is the effect of microalloying and tensile deformation on the internal structure (i.e. nanoscale precipitates and the stacking faults) in eutectic Si phase. The results show that the nanoscale precipitates are evident in eutectic Si phase in Al-Si alloy without any special heat treatment or modification. The additions of Sc and Zr into the Al-Si alloy increased the size of the nano precipitates, and significantly promoted the formation of the stacking faults inside the eutectic Si phase. Moreover, the eutectic Si phase experienced twinning deformation during the tensile deformation of the Al-Si based alloy, and this twinning deformation was more pronounced with increasing the tensile strength of the Al-Si based alloy. It is proposed that the deformation of the eutectic Si phase also contributed to the property and the ductility of the Al-Si based alloy.

Tailored precipitation route for the effective utilisation of Sc and Zr in an Al-Mg-Si alloy

In this work, we develop and assess two potential heat treatment methods tailored for the effective utilization of Sc and Zr in an Al-Mg-Si model alloy. (Al,Si)3(Sc,Zr) dispersoids and MgSi precipitates were identified and characterised using a combination of SEM, STEM and APT. The dispersoid composition and structure changed significantly depending on the heat treatment route. The strength increment due to Sc and the effectiveness of the heat treatments after hot extrusion and artificial ageing was determined using tensile tests. A tensile yield strength increase of approximately 60 MPa could be attained through the addition of 0.05 wt.% Sc and 0.1 wt.% Zr, provided a suitable heat treatment methodology was utilised. An analytical strengthening model was utilised to confirm the individual strengthening contributions of the (Al,Si)3(Sc,Zr) dispersoids and the various other active strengthening mechanisms in the final product. The strength increase from Sc and Zr additions to Al-Mg-Si was found to come from precipitation hardening owing the presence of nano-sized dispersoids. The (Al,Si)3(Sc,Zr) dispersoids were also revealed to act as preferential nucleation sites for the β’’ precipitates. These results can be used as an outline for the design of a suitable heat treatment for Sc and Zr augmented Al-Mg-Si alloys.

The effect of Sc addition on the novel nano-AlCu phase in as-cast Al-5%Cu alloy

The effects of Sc addition on the primary α-Al phases and novel nano-AlCu phases were investigated in Al-5%Cu alloys without and with 0.8%Sc. The microstructural evolution was characterized by scanning electron microscopy (SEM) and transmission electron microscope (TEM) with energy dispersive X-ray spectroscopy (EDS). In the study, the novel ribbon nano-AlCu phases were found in as-cast Al-5%Cu alloy and the average length is about 200–300 nm. When 0.8%Sc was added into the Al-5%Cu alloy, the α-Al phases were obviously refined from coarse dendrites to fine equiaxed grains and the average grains size decreased to 29.8 μm. Moreover, the number of nano-AlCu phases significantly increases, but the length and width obviously decrease. In addition, the nano-AlCu phases have a good lattice matching relationship with α-Al phases, which can act as a precursor refining α-Al grains.