As-cast State Research Articles

Regulating microstructure and mechanical properties of the as-cast Mg-4Zn-0.5Y-0.5Nd alloy by heat treatment

The Mg-4Zn-0.5Y-0.5Nd alloy was designed and fabricated by conventional casting with subsequent heat treatment to regulate the microstructure and mechanical properties. The microstructure, secondary phase, mechanical properties, and fracture behavior were analyzed to elucidate the influencing mechanism. The results reveal that the as-cast alloy is composed of equiaxed grains with large sizes and discontinuously distributed secondary phases. Moreover, the secondary phase is mainly W-Mg3Zn3Y2, which partly forms the eutectic structure. The solid solution treatment coarsens the equiaxed grains and transforms the secondary phase into near continuous distribution. The Mg41Nd5 phase appears and volume fraction of secondary phase decreases a little. The combining of solid solution and aging treatment increases grain size and volume fraction of secondary phase more or less. Furthermore, the Mg24Y5 phase appears and secondary phases have been changed into semi-continuous distribution. After heat treatment, the average grain size reaches its maximum value of 107.18 μm, and the volume fraction of secondary phase climbs up to 2.73 %. Moreover, the solid solution treatment weakens the crystallographic orientation preference along {0001} but induces diversified crystallographic orientation preference. The heat treatment increases microhardness from 57.2 HV0.1 of the as-cast state to 70.5 HV0.1 of the heat-treated state. Comparatively, the solid solution treatment decreases mechanical properties, while the solid solution and aging treatment increase strength and ductility simultaneously. Especially for the ductility, it has been improved by more than 80 %, which is beneficial to the subsequent thermalmechanical processing greatly.

Magnetic hysteresis of Sm1-x Gdx Co3 Cu2 alloys

The paper presents the results of a comprehensive study of the hysteresis characteristics of Sm1−𝑥Gd𝑥Co3Cu2 alloys (x=0.1–0.9), considering their actual microstructure. It is shown that in the as-cast state, all alloys in the series are significantly heterogeneous and contain inclusions of up to three phase components. Hightemperature annealing at 1050∘C for 4 hours enables modifying the microstructure of the original alloys, however, a single-phase state was only achieved for alloy samples with 𝑥 = 0.1. The high-coercivity state of the samples is provided by a regular microstructure and is implemented through the pinning mechanism. The maximum coercive force of 0.94 T was achieved on the Sm0.4Gd0.6Co3Cu2

Developing high elongation of Ca-containing Zn alloys with superior osteogenic and antibacterial properties

The development of high-strength zinc (Zn) alloys significantly contributes to the field of orthopedics by enhancing their osteogenic properties. Calcium (Ca) is pivotal for bone composition; however, its incorporation into the Zn matrix often hampers elongation due to the formation of large-sized CaZn13 phases. In this study, two Zn alloys with different Ca contents were prepared, and their microstructures, mechanical properties, corrosion behavior and biocompatibility were investigated. Results indicate that the Zn alloy with high Ca content exhibits large-sized and high-volume-fraction CaZn13 phases, which do not significantly change during equal channel angular pressing (ECAP). The grain sizes of ECAPed Zn alloys decreased from 36.75 μm and 35.81 μm of as-cast state to 4.32 μm and 1.71 μm, respectively. Refined microstructures contributed to the improvement of mechanical properties of Zn alloys, which have elongation over 15 % higher than that of all Zn-Mg-Ca alloys reported so far. The high elongation of Zn alloys originates from the inhibition of the propagation of microcracks which generated from the Zn/CaZn13 interphase. Moreover, the formation of large-sized CaZn13 phases leads to the severe local corrosion through enhancing galvanic effect, finally increasing corrosion rate. During degradation, the release of metallic ions, such as Zn2+, Mg2+, and Ca2+, are beneficial to the cell viability and osteogenic properties. And the accelerated release of Zn2+ plays a role in antibacterial performance. These results are very helpful for promoting the application of biodegradable Zn alloys in the field of orthopedics.

Enhancing magnetostriction in FeAl alloys via crystal growth orientation tuning by a trace amount of Pt doping

Iron-based cubic alloy systems opened the door to the development of magnetostrictive materials with moderate magnetostriction, low cost, and good mechanical properties. At the as-cast state, the grain growth orientation of these alloy systems is close to random, which deteriorates magnetostriction. Doping with certain elements can tune the growth orientation to enhance magnetostriction. However, the driving force for the crystal growth along preferential orientation is still not clear. Here in this work, revealed by density functional theory (DFT) calculation, Pt doping can tune the crystal growth direction of FeAl along <100> crystal direction (same as easy magnetization direction), which can be utilized to realize 90° domain-switching and thus magnetostriction is enhanced greatly. These are confirmed by experimental results. The magnetostriction increases from 29 ppm to 80 ppm, representing a 176% enhancement through doping with 0.4 at.% Pt. The maze magnetic domain structures, observed by magnetic force microscope, are also preferentially <100> oriented and feature stripes. In consideration of the similarity between this study and our previous study on FeGa alloy (C. Zhou et al., 2020), it can be expected that our methods can be extended to other magnetostrictive materials and help develop polycrystals with desired orientations.

Enhancing mechanical properties in Ti-Containing FeMn40Co10Cr10C0.5 High-Entropy alloy through Chi (χ) phase dissolution and precipitation hardening

This research investigates the effects of adding 2 at.% Ti on the microstructure, phase transformation, and mechanical properties of FeMn40Co10Cr10C0.5 high-entropy alloy (HEA) in both as-cast and homogenized conditions. The incorporation of Ti increased the lattice parameter of the FCC matrix and caused greater lattice distortion (∼5.9 %) due to the larger atomic radius of Ti. The negative mixing enthalpy of Ti resulted in segregation at interdendritic regions, forming a Ti-rich Chi (χ) phase during solidification. The as-cast structure displayed a dendritic microstructure consisting of 77.9 % FCC, 20.6 % χ, and 1.5 % TiC phases. After homogenization at 1200 °C for 2 h, the χ phase was dissolved, increasing the volume fraction of TiC to 24 %. The homogenized sample exhibited a substantial improvement in tensile properties, i.e., with the ultimate tensile strength (UTS) rising from 631 MPa in the as-cast condition to 689 MPa, and yield strength (YS) increasing from 346 MPa to 419 MPa, while maintaining an elongation of ∼ 54 %. These enhancements are attributed to solid solution strengthening, increased carbide precipitation, and the dissolution of the χ phase into the FCC matrix.

Constructing dilute Mg-1.0In binary alloy: A pathway to enhanced anode performance in Mg-air battery

Magnesium anode is a critical material in Mg-air battery; however, the contradiction between mitigating self-corrosion and promoting activation poses a significant obstacle to the rapid advancement of primary magnesium batteries. Herein, this issue is addressed by constructing a dilute Mg-1.0In binary alloy with 1 wt% indium as the anode material. The equiaxed dendrites and moderate indium concentration gradient in the as-cast anode facilitate the formation of a protective surface film, leading to a low corrosion rate of 0.20 mm y−1 and enhancing the stability prior to discharge. Moreover, during the battery discharge process, this unique microstructure enables the redeposition of metallic indium and indium hydroxide, thereby dramatically accelerating the shedding of oxidation products and suppressing side hydrogen evolution reaction. The Mg-1.0In anode in a Mg-air battery delivers a discharge capacity of 1587 mA h g−1 and an average voltage of 1.46 V at 10 mA cm−2, outperforming most of previously reported magnesium anodes and the control samples with various indium contents. This work would inspire the achievement of superior Mg-air battery performance through the use of binary magnesium anode system in as-cast state, as opposed to a more complex and time-consuming multi-component anode design involving heat treatment and plastic deformation.

Influence of hot forging on grain formation in Al0.35CoCrFeNi high-entropy alloy: numerical simulation, microstructure and mechanical properties

One-step (F100) and three-step (F30-60-40) hot forging of Al0.35CoCrFeNi alloy was investigated to achieve a uniform equiaxed grain structure. In the as-cast and forged state, only a single-phase face-centered cubic structure was observed. The formation of twins, recrystallized and partially recrystallized grains in the volume of the samples was observed depending on used forging process. To predict uniform grain-size formation numerical simulation of the hot-forging process was used. The numerical model was calibrated and validated by means of measured compression experimental data of as-cast Al0.35CoCrFeNi alloy before forging. Thermal analysis using finite element analysis was used to simulate cooling of sample during the relocation from the furnace on the lower die. Simulations were run under different thermo-mechanical conditions and the regions for the formation of dynamically recrystallized grains were predicted. Room temperature mechanical properties were evaluated after F100 and F30-60-40 hot-forging process. The F30-60-40 hot forging optimized the grain size, which was evident in the very small dispersion of the room temperature mechanical properties in tension. Elongation after F30-60-40 hot forging increased by 17%. The correlation between temperature, equivalent stress, equivalent plastic strain, microstructure, tensile properties, and strain-hardening behavior is discussed.

Directionally solidified NiCoCrFeAlW eutectic high-entropy alloy: Microstructure and mechanical properties

The NiCoCrFeAlW eutectic high-entropy alloy exhibits a balanced combination of ductility and strength. This study examines the microstructure evolution and mechanical properties of the Ni30Co30Cr10Fe10Al18W2 alloy at varying growth velocities (10, 20, 50, 100, and 200 μm/s), which in its as-cast state, features a microstructure that includes both coarse dendrites and lamellar eutectic. The structure of the coarse dendrites is characterized by an ordered body-centered cubic (B2) phase, while the lamellar eutectic, features a combination of face-centered cubic (FCC) and ordered B2 phases. The microstructure, characterized by lamellar and dendritic structures that are parallel to the growth direction after directional solidification, undergoes a morphological transition at the solid-liquid interface from a planar to a dendritic form as growth velocity increases. The tensile fracture strength initially increases with the growth velocity, reaching a peak of 1286 MPa at a velocity of 50 μm/s, and then subsequently decreases as the growth velocity continues to increase. Directional solidification results in an increase in sample elongation with increasing growth velocity, achieving an elongation of 22.5% at 200 μm/s. An examination of the deformation mechanism reveals that the lamellar structure, composed of the more ductile FCC phase and the harder B2 phase, effectively harmonizes the plasticity and strength of the alloy. Therefore, directional solidification significantly adjusts the eutectic microstructure's orientation, thereby enhancing the mechanical properties along the direction of solidification.

Revealing the substantial impact of trace Mg addition on the microstructural configuration of a cast Al-Li-Cu-Zr alloy under various conditions

In this study, the impact of 0.2 wt% Mg addition on the microstructural configuration of a cast Al-2.5Li-2.5Cu-0.15Zr alloy under different heat treatment conditions was investigated using multiscale characterization. Results indicate that in the as-cast state, trace Mg forms the low-melting-point Al2CuMg eutectic phases and promotes grain refinement. In the natural aging state, trace Mg promotes the precipitation of fine Guinier-Preston (GP) zones independent of pre-existing δ′-Al3Li phases. In the artificial aging state, trace Mg mainly leads to the inducing of GP zones, suppression of θ′-Al2Cu phases, and promotion of T1-Al2CuLi phases. δ′ phases with slight diameter reduction and minimal S′-Al2CuMg phases with two variants are also observed. Atomic-level analysis of the two newly formed composite precipitates indicates that L12 structure phases on both sides of the GP zone have an anti-phase relationship. This study is expected to provide theoretical insights into the microstructural origins underlying the beneficial effects of Mg microalloying in cast Al-Li-Cu alloys.

A novel BCC-L21-BCC hierarchical heterostructure high entropy alloy with excellent corrosion resistance and mechanical properties in as-cast state

In this paper, a novel as-cast CrFeNiAl0.35Si0.1Ti0.1 high entropy alloy (HEA) with micron-to-nano hierarchical heterostructure was designed, and its microstructure, mechanical properties and corrosion resistance have been systematically investigated. It is found that, this novel HEA exhibits well-dispersed L21 phases with various sizes from micron-scale to nano-scale in the BCC matrix, while nano-sized BCC lamellas could also emerge in the L21 phase with large diameter. Moreover, this HEA exhibits not only excellent corrosion resistance in 3.5 wt.% NaCl solution that close to super-stainless steels, but also high mechanical properties combining yield strength of 1712±56 MPa, compressive plasticity of 21.2%±0.5% and hardness of ∼560 Hv. Such outstanding comprehensive properties for this HEA are possibly resulted from the complex hierarchical BCC-L21-BCC heterostructure with stable passive film and low diversity in work function between different phases. This work provides a novel route in the development of high-performance corrosion-resistant HEAs for structural and coating applications.

Enhancing damping properties of Mg–Sn–Y alloys: The role of metastable clustering

The damping properties of Mg–Sn–Y alloys with varied Sn/Y atomic ratios and heat-treatment processes have been studied. In the as-cast state, the alloy with a Sn/Y ratio of 3:1 exhibits the highest damping property in the low strain region due to the low Y solid solution and small lattice distortion. After heat treatment with 480 °C and 24 h, the lattice distortion of the alloy with a Sn/Y atomic ratio of 1:1 is significantly reduced compared to the cast alloy, resulting in an ultra-high damping property in the low strain region (ε = 10−4, Q−1 = 0.023). This change in damping property is attributed to the presence of metastable clusters, which consume energy through atomic rearrangement, separation, and redissolution, thereby enhancing the damping property. However, excessively long heat treatment times or high temperatures are detrimental to the formation of these metastable clusters, leading to a decreased damping property.

Microstructural evolution and corrosion behavior of non-isothermally heat treated hypoeutectic Al-Si-Cu alloy

In the present work the effect of non-isothermal heat treatments on the microstructure and corrosion resistance of a hypoeutectic Al-Si-Cu die-cast alloy was studied. The microstructural aspects were examined by confocal laser scanning microscopy and scanning electron microscopy. The corrosion behavior was studied by potentiodynamic polarization tests. In the as-cast condition, the microstructure consisted of needle-like Si particles and Fe-rich intermetallics, besides the Al matrix. The non-isothermal treatments promoted spheroidization of Si particles, decreasing its volume fraction. The corrosion resistance was affected by concentration of the Si particles. The corrosion mechanism is discussed based on the microstructural evolution of the Al-Si-Cu alloy. The main influencing factor was the volume fraction of Si particles. The non-isothermally treated samples exhibited lower corrosion current density than the as-cast alloy, showing superior corrosion resistance.

Investigating the Impact of Robotic Milling Parameters on the Surface Roughness of Al-Alloy Fabricated by Wire Arc Additive Manufacturing

This paper takes the single-wall wall manufactured by wire arc additive manufacturing (WAAM) as the research object and compares it with the as-cast aluminum alloy with the same series. By using feed rate, cutting depth, spindle speed, etc., as single or compound parameters, the machinability of the sample is analyzed. The results indicate that the influence of varying parameters on the as-deposited aluminum alloy follows the order of feed rate &gt; cutting depth &gt; spindle speed. As the feed rate increases, the surface roughness initially decreases and then increases, with the optimal surface quality achieved at 12 mm/s (with a surface roughness of 2.013 μm). Different from the as-deposited alloy, the influence of the parameters on the as-cast alloys follows the order of spindle speed &gt; cutting depth &gt; feed rate. The experiments reveal that, for both as-deposited and as-cast states, the trends of the impact of cutting depth and spindle speed on surface quality are consistent. However, at low feed rates (2–12 mm/s), for as-deposited states, the surface quality of as-deposited samples becomes smoother as the feed rate increases (contrary to common knowledge). This result can be attributed to the elevated milling temperature, which softens the material, making it easier to remove and reducing the surface roughness.

Microstructural refinement of an Al-Ce-Mg alloy via Shear Assisted Processing and Extrusion

Al-Ce alloys have attracted recent interest because of their high thermal stability due to the low solubility of Ce in the Al matrix. The Al11Ce3 eutectic phase gives excellent strain hardening behavior and moderate high-temperature strength in the as-cast state. However, its strengthening effect is limited by its coarse as-cast structure. Therefore, alternative manufacturing methods such as additive manufacturing or equal channel angular pressing have been applied to refine the Al11Ce3 phase to good effect. However, these techniques are both expensive and time-consuming. Therefore, this study aims to use Shear Assisted Processing and Extrusion (ShAPE), an emerging solid phase processing technique that is more easily scalable than the previously mentioned methods. ShAPE can produce useful cross-sections of an Al-8Ce-4Mg alloy while refining the Al11Ce3 phase to produce a higher strength material. It was found that a low temperature ShAPE process can improve the room temperature yield strength by ∼60 % compared to a binary Al-4Mg alloy. Additionally, the high-temperature yield strength of the Al-Ce alloys increased by 20 %, with a simultaneous 15 % improvement in ductility compared to the binary Al-Mg alloy. These results highlight the potential for ShAPE as a processing technique for Al-Ce alloys.

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.

Development of Heat Treatments for Structural Parts in Aluminium Alloys Produced by High-Pressure Die Casting (HPDC)

In this work, we intended to study the effect of heat treatments (T5 and flash T6) on blistering, mechanical properties and microstructure for different parts produced by vacuum-assisted HPDC. These parts were produced with primary and secondary aluminium alloys (AlSi10MnMg alloy and AlSi10Mg(Fe) alloy, respectively). The parts presented blisters for all combinations of temperature (between 360 °C and 520 °C) and stage times (15 and 30 min) of solution heat treatments. However, when subjected to the T5 heat treatment, blisters were no longer visible. With this heat treatment, there was an increase in yield strength of 64% for both aluminium alloys and an increase in UTS of 31% in AlSi10Mg(Fe) alloy and of 24% in AlSi10MnMg alloy, when compared to the mechanical properties in the as-cast state. However, there was a decrease in ductility. The AlSi10Mg(Fe) alloy presented a lot of contaminations (especially iron), which impaired the mechanical properties compared to the primary aluminium alloy, AlSi10MnMg.

Microstructure evolution and properties of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloy prepared by SIMA

The semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys were prepared by strain induced melting activation method (SIMA), and the microstructure evolution, mechanical properties and corrosion resistance of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys were investigated. The results indicate that the ideal globular or near-globular microstructures with an average grain size of 29.1 μm and a shape factor of 0.86 can be obtained when the Al80Mg5Li5Zn5Cu5 light weight high entropy alloys with 20% deformation held at 500 °C for 15 min. The coarsening coefficient is 35.8 μm3/s when the temperature is 500 °C, which is lower than the traditional single major element alloys due to the sluggish diffusion effect of high entropy alloys. The compression strength of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys is 558.4 MPa, which is 11% higher than that of as-cast state. The corrosion resistance of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys is also significantly improved.

Effects of Co/Ni ratio on microstructure and mechanical properties of as-cast Cr-Fe-Ni-Co-Al-Si-Ti-Cu high entropy alloys

In this paper, partial replacement of Ni for Co was adopted in FCC + BCC heterostructure as-cast CrFeNi1-xCoxAl0.28Si0.09Ti0.02Cu0.01 high entropy alloys (HEAs), and the modification in microstructure and mechanical properties of these alloys with the increase in the Co/Ni ratio has been systematically investigated. It was observed that all these designed HEAs consist of FCC sideplates with a surrounding BCC phase, as well as well-dispersed B2 phase in as-cast state. Additionally, higher Co/Ni ratio leads to a larger proportion of BCC phase, which has following impacts on the mechanical properties of this series of HEAs: when such ratio begins to increase, it has obvious enhancement in strength and gradual decrease in plasticity; when it reaches 0.15/0.85, it has high strength of ∼1.4 GPa and good plasticity of >10 %. While further enhancing Co/Ni ratio leads to significant connection of BCC phase, resulting in drastic increase in brittleness. The detailed mechanism for such phenomenon has been discussed in detail. This study provides a novel route on improving the comprehensive mechanical properties of this series of as-cast HEAs.

A single-phase Nb25Ti35V5Zr35 refractory high-entropy alloy with excellent strength-ductility synergy

Refractory high entropy alloys (RHEAs) are promising candidates for high-temperature structural materials due to their excellent high-temperature performance. However, the room-temperature brittleness of most alloys results in poor plastic formability, thereby limiting their engineering applications. In this study, Nb25Ti35V5Zr35 alloy with cold-rollability was developed, and its phase stability, tensile mechanical properties, elastic properties, strengthening mechanism, and deformation mechanism were investigated by combining experiments, CALPHAD, DFT and molecular statics (MS) methods. The results demonstrate that Nb25Ti35V5Zr35 alloy possesses good phase stability, with both the as-cast and annealed states maintaining a single-phase BCC structure without undergoing phase transformation. The tensile yield strength of the alloy reaches its peak at 1152 MPa in the cold-rolled condition, while its annealed state exhibits an optimal balance of strength and plasticity, with a yield strength of 836 MPa and an elongation of 22.45 %, respectively. Solid solution strengthening is the primary source of its high strength, with V and Zr playing key roles in this strengthening mechanism. Dislocation slip plays a dominant role in plastic deformation. Additionally, compared to traditional BCC alloys, the significance of edge dislocations in the deformation process is notably enhanced, with the {112} plane serving as the preferred slip plane for dislocations. DFT results indicate that the alloy exhibits significant anisotropy in both Young's modulus and shear modulus. This work contributes to understanding the material properties of the Nb25Ti35V5Zr35 alloy and provides a reference for the design of new ductile RHEAs.

Microstructure and Properties of Complex Concentrated C14–MCr2 Laves, A15–M3X and D8m M5Si3 Intermetallics in a Refractory Complex Concentrated Alloy

Abstract: The refractory complex concentrated alloy (RCCA) 5Al–5Cr–5Ge–1Hf–6Mo–33Nb–19Si–20Ti–5Sn–1W (at.%) was studied in the as-cast and heat-treated conditions. The partitioning of solutes in the as-cast and heat-treated microstructures and relationships between solutes, between solutes and the parameters VEC and Δχ, and between these parameters, most of which are reported for the first time for metallic UHTMs, were shown to be important for the properties of the stable phases A15–Nb3X and the D8m βNb5Si3. The nano-hardness and Young’s modulus of the A15–Nb3X and the D8m βNb5Si3 of the heat-treated alloy were measured using nanoindentation and changes in these properties per solute addition were discussed. The aforementioned relationships, the VEC versus Δχ maps and the VEC, Δχ, time, or VEC, Δχ, Young’s modulus or VEC, Δχ, nano-hardness diagrams of the phases in the as-cast and heat-treated alloy, and the properties of the two phases demonstrated the importance of synergy and entanglement of solutes, parameters and phases in the microstructure and properties of the RCCA. The significance of the new data and the synergy and entanglement of solutes and phases for the design of metallic ultra-high temperature materials were discussed.