Sc Addition Research Articles

Improvement in the mechanical properties and creep resistance of Al-Mn-Mg 3004 alloy with Sc and Zr addition

Sc and Zr were added to Al-Mn-Mg 3004 alloy to form two populations of strengthening particles (50–70 nm-sized α-Al(Mn,Fe)Si dispersoids and 6–8 nm-sized Al3(Sc,Zr) precipitates), and their strengthening effects on the mechanical properties and creep resistance at ambient and elevated temperatures were studied. The results showed that the microhardness and yield strength at ambient temperature greatly increased upon the addition of Sc and Zr. The creep resistance at 300 °C significantly improved due to the precipitation of fine Al3(Sc,Zr) particles and reduction of the particle-free zone. However, the yield strength at 300 °C remained constant even though the Sc and Zr content increased. The combined effects of α-Al(Mn,Fe)Si dispersoids and Al3(Sc,Zr) precipitates on the yield strengths at 25 °C and 300 °C were quantitatively analyzed based on the Orowan bypass and dislocation climb mechanisms. The analytically predicted yield strengths are in good agreement with the experimental data.

Effects of Zr, Ti and Sc additions on the microstructure and mechanical properties of Al-0.4Cu-0.14Si-0.05Mg-0.2Fe alloys

The evolution of microstructure and mechanical properties of Al-0.4Cu-0.14Si-0.05Mg-0.2Fe (wt.%) alloys, micro-alloyed with Zr, Ti and Sc, were investigated. The addition of 0.2%Zr to base alloy accelerates the precipitation of Si-rich nano-phase in α-Al matrix, which plays an important role in improving the mechanical properties of an alloy. The tensile strength increases from 102MPa for the base alloy to 113MPa for the Zr-modified alloy. Adding 0.2%Zr+0.2%Ti to base alloy effectively refines α-Al grain size and accelerates the precipitation of Si and Cu elements, leading to heavy segregation at grain boundary. By further adding 0.2%Sc to Zr+Ti modified alloy, the segregation of Si and Cu elements is suppressed and more Si and Cu precipitates appeared in α-Al matrix. Accompanied with the formation of coherent Al3Sc phase, the tensile strength increases from 108MPa for the Zr+Ti modified alloy to 152MPa for the Sc-modified alloy. Due to excellent thermal stability of Al3Sc phase, the Sc-modified alloy exhibits obvious precipitation hardening behavior at 350°C, and the tensile strength increases to 203MPa after holding at 350°C for 200h.

Effect of trace amounts of added Sc on microstructure and mechanical properties of 2055 aluminum alloy

The effects of Sc additions and isothermal aging on the microstructure and mechanical properties of 2055 aluminum alloy have been investigated. The isothermal aging temperatures investigated were 175 °C and 200 °C. Results show that the aging temperature does not affect the type of precipitates in both Sc-free and Sc-added 2055 Al alloys. While remarkable changes in the size and number density of T1 (Al2CuLi) precipitates have been observed. For samples aged at 175 °C for 8 h, the average length of T1 precipitates was increased from 39.9 nm to 45.6 nm, the number density decreased from 5.77 × 1022 m−3 to 3.68 × 1022 m−3 after Sc addition. On the contrary, when samples were aged at 200 °C for 8 h, the length decreased from 59.89 nm to 43.32 nm and number density increased from 2.13 × 1022 m−3 to 3.00 × 1022 m−3 by adding trace Sc. Slight deterioration of tensile strength and yield strength with higher ductility was founded at the aging temperature of 175 °C for 8 h due to the larger size and lower number density of T1 precipitates along with the formation of a W (AlCuSc) phase during the casting or homogenization processes. When aging temperature increased to 200 °C, tensile strength and yield strength were significantly improved by Sc addition without losing ductility. Highly dense fine T1 precipitates take responsible for the strength improvement, and to some extent it compensated the strength loss caused by the formation of W phase. A “vacancy-prison” mechanism was adopted to explain the effect of Sc additions on the precipitation of T1 phase as a function of aging temperature.

Characterisation of AlScZr and AlErZr alloys processed by rapid laser melting

AlScZr and AlErZr alloys with Sc or Er additions of ~0.6 at.% were prepared by a novel wedge mould casting and laser remelting methodology. Precipitation strengthening and thermal stability were studied using hardness testing and transmission electron microscopy. After ageing, the AlScZr alloy achieved a peak hardness of 113HV0.5 and possessed pronounced thermal stability, while the AlErZr alloy obtained a maximum hardness of 84HV0.5 and experienced relatively rapid over-ageing. Compared with Sc, the lower solubility of Er even after laser remelting and its more rapid diffusivity are responsible for the relatively lower ageing response and poorer thermal stability.

Influence of Scandium Addition on Stress Corrosion Cracking Susceptibility of Al-Zn-Mg Alloy in Different Corrosive Environments

Stress corrosion cracking (SCC) susceptibilities of Al-Zn-Mg alloys without and with Scandium addition were evaluated in 3.5% NaCl solution at different pH and different strain rate, using slow strain rate test technique. The results indicate that Sc addition reduces grain size and width of precipitation free zones, and transforms grain boundary precipitates from continuous distribution into interrupted distribution by inhibiting recrystallization. In solution at pH 1, pH 3 and pH 7, Sc addition reduces the degree of localized corrosion of alloy surface and SCC susceptibility of Al-Zn-Mg alloy. However, in solution at pH 10 and pH 12, grain refinement significantly promotes the diffusion of hydrogen atoms into matrix, thus Sc addition increases SCC susceptibility of Al-Zn-Mg alloy. Under different strain rate conditions, Sc addition can all reduce SCC susceptibility of Al-Zn-Mg alloy in solution at pH 1, pH 3 and pH 7, and can all increase SCC susceptibility of Al-Zn-Mg alloy in solution at pH 10 and pH 12. As a result, Sc modified Al-Zn-Mg alloy in practical applications should be avoided in alkaline environments.

Effect of Trace Be and Sc Additions on the Mechanical Properties of A357 Alloys

The effect of the addition of Be and Sc on the microstructure and mechanical properties of A357 alloy were systematically investigated. The results show that the addition of small amounts of Be and Sc could change the acicular structure of iron-bearing intermetallic compounds to harmless compact Al-Fe-Si and Sc-Fe iron-bearing intermetallic compounds. Compact iron-bearing intermetallic compounds could improve fluidity, causing a reduction in interdendritic shrinkage during solidification. The addition of 0.05 wt % Be enhanced the quality index of the A357 alloy by 11% and increased the notch-yield ratio of fracture toughness by 4.5%. In contrast, the addition of 0.05 wt % Sc increased the quality index and the notch to yield ratio of fracture toughness up to 17% and 9%, respectively. Therefore, the microstructure and mechanical properties of the A357 alloy could be improved by substituting Be with Sc.

Effects of the addition of trace amounts of Sc on the microstructure and mechanical properties of Al-11.6Si alloys

The effects of the addition of trace amounts of scandium on the microstructure and mechanical properties of Al-11.6Si alloy were investigated. The results show that the iron-bearing phase of Al-11.6Si alloy without the addition of Sc in the aluminum matrix was present in the acicular form. This acicular iron-bearing phase is a hard and brittle intermetallic compound that is easily broken during the solidification process, causing serious damage in the mechanical properties (especially the ductility) of the alloy. During thermal exposure to high temperature at 250 °C for 100 h, the Al-11.6Si alloy without the addition of Sc undergoes recovery and recrystallization, reducing the mechanical strength. However, trace amounts of Sc transform the acicular iron-bearing phase of Al-11.6Si alloy into the chinese-script iron-bearing phase, thereby reducing the length and the amount of the iron-bearing phase. These factors enhance the ductility of Al-11.6Si alloy with Sc addition. In addition, it was remarkably found that a high density of L12-ordered Al3Sc precipitates are formed during thermal exposure at 250 °C for 100 h in Al-11.6Si alloy with Sc addition. The precipitation of L12-ordered Al3Sc precipitates effectively inhibited grain growth and hindered the movement of dislocations. These factors led to the Sc-containing alloy having the best mechanical properties (strength and ductility) than Al-11.6Si alloy without Sc addition during the following thermal exposure at 250 °C.

Grain size-dependent Sc microalloying effect on the yield strength-pitting corrosion correlation in Al-Cu alloys

Coarse-grained (CG), fine-grained (FG), and ultrafine-grained (UFG) Al-2.5 wt% Cu (Al-Cu) alloys were respectively prepared, with and without 0.3 wt% Sc addition, for comparison. The influences of minor Sc addition on the microstructural evolution, tensile mechanical properties and pitting corrosion resistance were systematically studied at different grain scales. A significant Sc microalloying effect on the precipitation was observed that the minor Sc addition promoted the dispersion of finer θ′-Al2Cu precipitates in the CG alloy and favored the intragranular θ′-Al2Cu precipitation in the FG and UFG alloys, with the smaller grain size leading to a stronger Sc microalloying effect. The Sc addition induced convincing increases in the yield strength at all the three grain scales, and improved (in the CG and UFG Al-Cu alloys) or retained (in the FG Al-Cu alloy) the pitting corrosion resistance at the same time. This indicates that the inverse strength-pitting corrosion correlation as usually observed can be broken by minor Sc addition. The strengthening mechanisms were discussed and the grain size-dependent pitting corrosion resistance mediated by the Sc addition was rationalized in terms of a competition between the positive influence derived from the interfacial Sc segregation and the negative influence come from the deformation-induced dislocations. The present findings provide a possible approach to break the inverse strength-pitting resistance correlation in heat-treatable Al alloys by modifying the precipitate/matrix interfaces through the suitable microalloying atom segregation.

Fluidity and Hot Cracking Susceptibility of A356 Alloys with Sc Additions

A356 with scandium (Sc) addition provides interesting results beyond costs. For the practical use of Sc, the effects of Sc on castability must be considered. Fluidity and hot cracking are important factors defining the castability of aluminum casting alloys. In the present work, the influence of Sc addition on the castability of A356 hypoeutectic Al–Si alloy was investigated, which was evaluated through fluidity and hot cracking susceptibility. The fluidity of the alloys was studied by measuring the total volume of solidified aluminum in a multi-channel mold. The hot cracking susceptibility of the alloys was evaluated by using a constrained-rod casting mold test. The results of the fluidity and hot cracking susceptibility test were supported by microstructural analysis. The results indicate that 0.2 wt% Sc addition significantly increases the fluidity of A356 alloy, due to the grain refinement and eutectic Si modification by changing the solidification mode. However, the fluidity slightly decreases when the Sc content increases to 0.4 wt% due to the formation of primary Al2Si2Sc intermetallic phase. The hot cracking of A356 alloy was completely diminished when Sc was added to the alloy.

Role of scandium additions in primary silicon refinement of hypereutectic Al–20Si alloys

ABSTRACT This study investigates the effect of Sc on the formation of primary silicon during the solidification of hypereutectic Al–20Si alloys. The evolution of the microstructure was studied using thermal analysis. The results show that the addition of 0·2 and 0·4 wt-% Sc suppresses the nucleation of primary silicon due to the formation of ScP particles instead of AlP particles. For large Sc additions, at the centre of the samples, the primary silicon has a star-shaped morphology with thin branches. The addition of Sc decreases the P refinement efficiency in hypereutectic Al–20Si alloys, which may be a result of the formation of a ScP phase. The results suggest that the addition of Sc poisons the nucleant particles of the primary and eutectic silicon.

The influence of Sc solute partitioning on ductile fracture of Sc-microalloyed Al-Cu alloys

Al-XCu (X = 1.0, 1.5, and 2.5 wt%) alloys with and without 0.3 wt% Sc addition were prepared respectively. The effects of composition and heat treatment processes on the microstructural evolution were systematically investigated by using transmission electron microscope and atom probe tomography (APT). Both Al3Sc dispersoids and θ′-Al2Cu precipitates coexisted after artificial aging, and a strong Sc segregation at θ′-Al2Cu/matrix interfaces was detected and quantified through APT examinations. A Sc solute partitioning was demonstrated between in the Al3Sc dispersoids and at the θ′-Al2Cu/matrix interfaces, mediated by the Cu content. Increasing the Cu content, both the size and volume fraction of the Al3Sc decreased after solid solution treatment. As a result, the interfacial Sc segregation was accordingly intensified during subsequent aging treatment. A parameter of reduction in interfacial energy (Δγ), derived from APT analyses, was proposed to characterize the degree of interfacial Sc segregation. The coupling effect of Al3Sc dispersoids and θ′-Al2Cu precipitates on ductile fracture was discussed, where a micromechanical model was developed to describe a quantitative relationship between the fracture strain with Δγ as well as parameters of the Al3Sc dispersoids.

Influence of Sc Addition on the Corrosion Behavior of Medium Strength Al-Zn-Mg Alloy

In this paper, the effect of Sc addition (0.06 wt%) on the corrosion behavior of medium strength Al-Zn-Mg alloy is investigated by mass loss measurements, electrochemical experiment, intergranular corrosion and exfoliation corrosion tests. The results indicate the addition of Sc reduces the relative weight loss and enhances pitting performance as a result of grain refinement. The improved intergranular corrosion and exfoliation corrosion resistance caused by minor Sc addition are mainly attributed to the delay in both the initiation and advance stages of local corrosion.

Effect of minor Sc on the microstructure and mechanical properties of AZ91 Magnesium Alloy

The as-cast and heat-treated microstructures and mechanical properties of the AZ91 magnesium alloys with and without minor Sc addition were investigated and compared in this paper. The results indicated that adding 0.15–0.45 wt% Sc to the as-cast AZ91 alloy not only could modify and refine the Mg17Al12 phase but also suppress the formation of the Mg17Al12 phase. At the same time, the grains of the Sc-containing as-cast AZ91 alloys were also effectively refined. As a result, the mechanical properties at room temperature (RT) for the Sc-containing as-cast AZ91 alloys were effectively improved. In addition, adding 0.15–0.45 wt%Sc to the AZ91 alloy promoted the formation of the continuous precipitates (CP) during the aging treatment in spite of that the formation of the discontinuous precipitates (DP) was simultaneously suppressed. Accordingly, the Sc-containing as-aged AZ91 alloys obtained the relatively higher mechanical properties at RT than the as-aged AZ91 alloy.

Influence of Sc on microstructure and mechanical properties of Al–Si–Mg–Cu–Zr alloy

In the present study, the effects of Mg, Cu, Sc and Zr combined additions on the microstructure and mechanical properties of hypoeutectic Al–Si cast alloy were systematically investigated. Characterization techniques such as optical microscopy (OM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), electron back-scatter diffraction (EBSD), atomic force microscopy (AFM), transmission electron microscope (TEM), Brinell hardness tester and universal testing machine were employed to analyze the microstructure and mechanical properties. The results showed that Sc served as modifier on the microstructure of Al–3Si–0.45Mg–0.45Cu–0.2Zr alloys, including modification of eutectic Si and grains. Extraordinarily, grain refinement was found to be related to the primary particles, which exhibited a close orientation to matrix. After T6 heat treatment, the grain structures were composed of nano-scaled secondary Al3(Sc, Zr) precipitates and spherical eutectic Si. Combined with T6 heat treatment, the highest hardness, yield strength, ultimate tensile strength and elongation were achieved in 0.56 wt.% Sc-modified alloy. Interestingly, the strength and ductility had a similar tendency. This paper demonstrated that combined additions of Mg, Cu, Sc and Zr could significantly improve the microstructure and performance of the hypoeutectic Al–Si cast alloy.

Remarkable increase in the rate of the catalytic epoxidation of electron deficient styrenes through the addition of Sc(OTf)3 to the MnTMTACN catalyst.

The effect of Lewis acids on the catalytic activity of [Mn2(μ-O)3(TMTACN)2](PF6)2 in the epoxidation of styrenes using hydrogen peroxide as the oxidant has shown that the addition of Sc(OTf)3 at low catalytic loading results in a very significant increase in the efficiency of the catalyst and a reduction of the reaction time to only 3 minutes in most cases.

Effect of Sc Addition on the Microstructure and Mechanical Properties of Melt-Spun Al-10Ni Alloys

Effect of Sc Addition on the Microstructure and Mechanical Properties of Melt-Spun Al-10Ni Alloys

Evaluation of microstructure, damping capacity and mechanical properties of Al-35Zn and Al-35Zn-0.5Sc alloys

Al-35Zn and Al-35Zn-0.5Sc alloys were fabricated in this study. The addition of 0.5 Sc promoted the grain refinement of the Al-35Zn alloys during solidification, heat treatment, and hot rolling. Dynamic precipitation also occurred in the Al-35Zn and Al-35Zn-0.5Sc alloys during rolling. The damping capacity and mechanical properties of the Al-35Zn alloy were improved by the Sc addition and hot rolling. The rolled Al-35Zn-0.5Sc alloy with 90% reduction demonstrated better damping capacity than those of commercial Al alloys and some metallic materials with high damping capacity, which is mainly attributed to the high interface sliding capacity. Compared with the commercial Al alloys, the rolled Al-35Zn-0.5Sc alloy with 90% reduction showed balanced mechanical properties, including high strength and reasonable ductility. This work provided an effective strategy for preparing Al alloys with excellent damping capacity and mechanical properties.

Magnetostructural phase transitions and magnetocaloric effect in (Gd5-xScx)Si1.8Ge2.2

Future advancements in magnetocaloric refrigeration/heat pumping technologies depend on the discovery of new materials that demonstrate large, tunable magnetocaloric effects (MCEs) in the vicinity of coupled magnetic and structural phase transitions that occur reversibly with minimum hysteresis. With this in mind, we investigate phase transitions, microstructure, magnetic, thermal, magnetocaloric, and transport properties of (Gd5-xScx)Si1.8Ge2.2 compounds. Replacement of magnetic Gd with non-magnetic Sc in Gd5-xScxSi1.8Ge2.2 increases the ferromagnetic to paramagnetic first order phase transition temperature, TC, with only a minor reduction in MCE when x ≤ 0.2. We also demonstrate that hydrostatic pressure further increases TC and reduces the hysteresis of the first order phase transition in Gd4.8Sc0.2Si1.8Ge2.2 from 7 to 4 K. Temperature-dependent x-ray powder diffraction study of Gd4.8Sc0.2Si1.8Ge2.2 confirms the monoclinic ↔ orthorhombic structural transformation at TC, in agreement with magnetic, calorimetric, and electrical transport measurements. In addition to the substantial magnetocaloric effect, a large magnetoresistance of ∼20% is also observed in Gd4.8Sc0.2Si1.8Ge2.2 for ΔH = 50 kOe in the vicinity of the magnetostructural transition. In a drastic reversal of the initial doping behavior further additions of Sc (x > 0.2) suppress formation of the monoclinic phase, change the nature of the transition from first-to second-order, and reduce both the transition temperature and magnetocaloric effect.

Effects of scandium addition on biocompatibility of biodegradable Mg–1.5Zn–0.6Zr alloy

Heretofore, the effects of scandium on the biocompatibility of biodegradable magnesium alloys are extremely limited recognized. In the present study, four Mg–1.5Zn–0.6Zr–xSc (x = 0, 0.2, 0.5, 1.0 wt%) alloys were fabricated and their hydrophilicity, cytotoxicity, and hemocompatibility were investigated. The contact angle measurements revealed that addition of Sc improved the hydrophilicity of the alloys. For biodegradable alloys, perfect hydrophilicity could promote the tissue attaching on implant surface, establishing a benign biological reaction and improving the therapeutic effectiveness. The viabilities of L-929 cells and SP2/0 cells for all the alloys were about 100% and 90% compared to negative control, respectively. No obvious differences existed in cell viabilities between different Sc contents. With increasing addition of Sc, the hemolysis percentages and the degree of platelet activation increased. It deteriorated the hemocompatibility of the alloys. Proteomics, genomics, and in vivo investigations are needed in the future to get more deep understandings of the biocompatibility of Sc.

Effects of pre-aging and minor Sc addition on the microstructure and mechanical properties of friction stir processed 7055 Al alloy

The effects of Sc addition and pre-aging on the microstructure and mechanical properties of friction stir processed (FSP) 7055 Al alloy were investigated. The addition of Sc effectively inhibited the coarsening of grains in the FSP 7055 Al alloy due to the grain boundary pinning effect of Al3(Sc,Zr) particles. The high density of Al3(Sc,Zr) particles also provided more preferential nucleation sites for the precipitation of the η phase during FSP, and then inhibited the coarsening and increased the density of the η phase in the FSP 7055 alloy. The η′ phase precipitated in the 7055 and Sc-containing 7055 during artificial aging, and then dissolved into the Al matrix during FSP. Thus, pre-aging effectively inhibited the formation of the η phase during FSP, and increased the quantity of the solute atoms in the FSP samples. The mechanical properties of the FSP 7055 Al alloy were improved by the addition of Sc and pre-aging. The aged 7055–0.25Sc Al alloy with FSP showed the highest ultimate tensile strength of 578 MPa; and the aged 7055 Al alloy with FSP showed the largest elongation of 21%. This work provides an effective strategy to improve the mechanical properties of FSP Al alloys.