Alnico Alloys Research Articles

Laser directed energy deposition of Alnico-8H from blended elemental powders: Effect of nickel increase on magnetic properties

Alnico-8H (14 wt% Ni) and Alnico-8H (19 wt% Ni) were additively fabricated from a blend of elemental powders with compositions (in wt.%) of 38Co-29Fe-14Ni-8Al-8Ti-3Cu and 33Co-29Fe-19Ni-8Al-8Ti-3Cu, respectively, using laser-directed energy deposition technique. Post additive fabrication both compositions were subjected to homogenization heat treatment at 1250 °C for 30 min and magnetic annealed at 650 °C under 2.5 T magnetic field for 60 mins (1 hr). X-ray diffraction was employed for studying the phase evolution. Scanning and transmission electron microscopes were utilized for characterization of Alnico alloys. The targeted compositions for Alnico-8H (14 wt% Ni) and Alnico-8H (19 wt% Ni) were nearly achieved in the L-DED processed samples. homogenization at 1250 °C, followed by magnetic annealing at 650 °C, resulted in an increase in grain size. The transmission electron microscopy revealed the presence of ferromagnetic α1 and paramagnetic α2 phases in the magnetic annealed microstructure. The increase in Nickel content from 14 to 19 wt% resulted in increase in coercivity (242 to 255 Oe), remanence (4437 to 8659 G), and maximum energy product (BHmax) (0.27 to 0.53 MGOe).

Effect of grain structure on the magnetic properties of AlNiCo 8 alloys

AlNiCo alloy has gained popularity again in recent years due to its good corrosion resistance, affordability, and superior performance at high temperature. However, the lower magnetic properties of AlNiCo limit its wide variety of applications. Directional solidification process is a key process that affects the properties of AlNiCo alloy. During the solidification process, grains with various structures are formed due to the difference of cooling rate at different positions of the ingot. As the cooling rate slows down, the average grain size gradually increases, and orientation degree of the grains becomes better, resulting in the increase of coercivity (Hc) and remanence (Br). Therefore, the top sample has the best Hc and Br, the bottom is the worst, and the middle is between the two. It is found that when the average grain size increases, the percentage of transverse grain boundaries and high angle grain boundaries (HAGBs) decrease, the truncated α1 phase decreases, and the Hc rises, whereas the magnetic moment along the easy-axis direction is not affected by the external magnetic field when the grain orientation coincides, and the Br value increases, and the Br value increases. Large and highly oriented grains are associated with excellent performance, providing a new method to enhancing magnetic properties by regulating the grain structure.

Effect of Alloying Elements on the Microstructure and Magnetic Properties of Mechanically Alloyed AlNiCo‐Based High‐Entropy Alloys

Herein, the effect of addition of Cu, Fe, and CuFe on microstructure and magnetic properties of equiatomic ternary AlNiCo alloy is reported. This addition of Cu, Fe, and CuFe to AlNiCo results in L12, B2, and mixed α + B2 phases, respectively, during the mechanical alloying (MA) and subsequent annealing process. The low‐temperature magnetic properties show that the addition of nonmagnetic Cu to AlNiCo enhances the coercivity, while Fe enhances the saturation magnetization value. Further from the study of magnetic properties, it is suggested that the phase segregation effects are minimum in MA process compared to melt process. It is also shown that the disorder plays a significant role in controlling the magnetic properties. The observed anomalous magnetic behavior is discussed in terms of modifications in exchange interactions between constituent elements due to chemical and structural disorder.

In-situ observation of magnetic domain reversal during magnetic viscosity of permanent magnets

Magnetic viscosity analysis is a widely studied topic in understanding the stability and magnetization mechanisms of magnets. However, observing the minute changes in magnetic domains during the magnetic viscosity process poses a challenge in research. To address this issue, a self-made in-situ magnetized sample holder was used in this study to observe the dynamic evolution of domain structures in alnico alloy during magnetic viscosity. The findings indicate that the domain reversal during magnetic viscosity is largely irreversible, with only minor reversible changes observed in the inhomogeneous region. The magnetization reversal in alnico alloy occurs through the reversal of α1 phases, which follows a single domain particle reversal mode. The zero-field activation energy (E0) of alnico alloy is determined as 3.30 × 10−17 J, and the coercivity field without thermal disturbance (H0) is measured at 1779.19 Oe. This research method proves to be a valuable tool in the study of magnetic materials.

Microstructure and magnetic properties of Dy-added Alnico alloys

Alnico permanent alloys are still irreplaceable and show great potential in high temperature applications considering their excellent thermal stability, while the market for Alnico alloys is limited by their low coercivity. Rare-earth addition has been shown to increase the coercivity of Alnico alloys. In this work, the effects of Dy-addition on the crystal structure, microstructure, spinodal decomposition phases and magnetic characteristics of Alnico alloys were systematically investigated. The results indicate that the Dy element forms Dy-rich precipitates and influences the morphology and composition of spinodal decomposition structure. The 0.3 wt% Dy addition improves the coercivity from 132 kA·m−1 for the Dy-free alloys to 141 kA·m−1 for the Dy-added alloys and slightly optimizes the thermal stability. The enhancement of coercivity is attributed to the refined and uniform spinodal decomposition structure by reducing the mismatch degree and coherency strain. However, the magnetic properties of the 0.6 wt% Dy added alloy decrease due to the damaged structure with excessive Dy-rich phases and more connected α1 phases. A method for improving coercivity and thermal stability is suggested.

Analyzing the Relationship between the Chemical Composition and the Surface Finish of Alnico Alloys in EDM.

The purpose of this study was to determine whether the chemical compositions of Alnico alloys had any effects on the electrical discharge machining (EDM) performance and the surface finish. This article compares the behavior of three different Alnico alloys in electrical discharge machining. The experiments were conducted under different conditions using a BP93L EDM machine (ZAP BP, Końskie, Poland), applying an additional rotary motion to the electrode. A Box-Behnken experimental design was employed to analyze the influence of three factors, i.e., the spark current, the pulse-on time, and the pulse-off time, at three levels for three Alnico alloys. The material removal rate (MRR) was calculated for the different process parameters. After the EDM, the surface roughness was studied using a Talysurf CCI Lite non-contact profiler (Taylor-Hobson, Leicester, UK). The next step of the experiments involved preparing metallographic specimens to be observed by means of scanning electron microscopy (SEM) and optical microscopy (OM). Measurements of the nanohardness were also performed. The experimental data were then analyzed using Statistica software version 10 (64-bit) to determine and graphically represent the relationships between the input and output parameters for the three Alnico alloys. The chemical compositions of the Alnico alloys affected the thickness of the white layer (higher cobalt content, lower white layer thickness) and the material removal rate. The higher the cobalt content, the thinner the white layer and the lower the material removal efficiency. Moreover, the cobalt content in Alnico alloys influenced the shape of the precipitates; these ranged from spheroidal (13% Co) to mix-shaped (21.3% Co) to flake-shaped (32.2%). The hardness of the resulting white layer was 874 HV at10 mN.

Observation of itinerant ferromagnetic behaviour in equiatomic medium entropy AlNiCo alloy

A medium entropy AlNiCo alloy has been synthesized by vacuum arc melting, which shows single phase B2 structure. Atom probe tomography analysis showed that the elements are homogeneously and randomly distributed in AlNiCo alloy without any clustering tendency. A detailed analysis of temperature and field dependent magnetization data suggests an itinerant ferromagnetic ground state of AlNiCo alloy. The magneto crystalline anisotropy is evaluated to be 1.03 × 105 ergs/cm3 at 5 K. A broad maximum at low temperature in zero-field-cooled (ZFC) magnetization, as well as irreversibility of ZFC and field-cooled (FC) curves indicated a glassy behavior. This observation is supported by the memory effects observed at low temperature. The observed anomalous magnetic behavior is discussed in terms of modifications in exchange interactions. To the best of our knowledge, this is the first report on microstructure and magnetic properties of an equiatomic ternary AlNiCo alloy.

Effect of spinodal decomposition structure of alnico alloy on magnetic viscosity and magnetization reversal

The slow decay of permanent magnet magnetization with storage time will greatly affect the accuracy of precision instruments. The alnico is a traditional permanent magnetic material with excellent stability, and the research on its stability cannot be ignored. Magnetic field heat treatment is a key process that affects the microstructure of the alnico alloy. The alnico alloys with different α1 phase orientations and aspect ratios were prepared by adjusting the magnetic field intensity during spinodal decomposition. With the increase of magnetic field strength, the aspect ratio of the α1 phase increases significantly, and the orientation becomes better, which leads to the increase of coercive force and remanent magnetization, but the magnetic viscosity coefficient decreases. The demagnetization process of alnico samples was characterized by Lorentz transmission electron microscopy (LTEM) and electron holography. At the magnetic field interval of 200 Oe, the area of irreversible magnetization reversal of the S3 is significantly larger than that of the S0. The first-order reversal curves (FORC) show that most the randomly oriented α1 phases are reversible magnetization reversal, and the interaction field is smaller than that of neatly arranged α1 phases. This structure results in better stability. The alnico alloy without a magnetic field during spinodal decomposition sacrifices some magnetic properties but obtains better stability, which provides a research direction for stabilizing treatment by adjusting microstructure.

Effects of EDM on the Chemical Composition and Microstructure of the Surface Layer of Alnico Alloys

Effects of EDM on the Chemical Composition and Microstructure of the Surface Layer of Alnico Alloys

Influence of EDM Process Parameters on the Surface Finish of Alnico Alloys.

This article deals with electrical discharge machining (EDM) of an alnico alloy, focusing on how key process parameters affect the surface finish. The experiments were conducted using a BP93L EDM machine. The Box–Behnken design was employed to study the effects of three factors, i.e., spark current, pulse-on time, and pulse-off time, each at three levels, on the surface quality. A specially designed system was employed to increase the effectiveness of the machining process by imparting an additional rotary motion to the tool and an additional rotary motion to the workpiece. The aim was to efficiently remove the eroded metal particles and create a surface with smaller craters. The workpiece surface roughness was measured with a Talysurf CCI lite non-contact profiler. During this precision machining process, the arithmetical mean height (Sa) was less than 1 µm. The surface quality was examined also using scanning electron microscopy (SEM) and optical microscopy (OM). The experimental data were analyzed by means of Statistica to determine and graphically represent the relationships between the input and output parameters.

The Effect of Selective Laser Melting Conditions on the Structure of an Alnico Alloy

The Effect of Selective Laser Melting Conditions on the Structure of an Alnico Alloy

Efficient extraction of aluminum from leaching solutions of waste alnico alloys by CA12-N235 system

• A green and efficient non-saponified CA12-N235 system to extract Al is presented. • Complete separation of Al from Ni and Co is obtained. • Extracted complex is AlA 3 bound with R 3 NH + via hydrogen bonding. • CA12-N235 system has advantage of quick phase for Al extraction. • High purity aluminum is obtained from recycling of waste alnico alloy. Waste alnico alloy contains valuable metals of aluminum, nickel and cobalt. Recycling of these metals is of great importance from the perspective of resource utilization. In this study, we present a green and efficient extraction system to separate aluminum from nickel and cobalt in the leaching solution of waste alnico alloy. Using the CA12-N235 system consisting of 30 vol% CA12, 25 vol% N235 and 45 vol% kerosene as the extractant, nearly 100% aluminum was extracted while only 6.1% cobalt and 6.7% nickel were co-extracted after two-stage extraction. The nickel and cobalt in the loaded organic phase were scrubbed completely by two-stage scrubbing with water. The high purity aluminum was obtained in the strip liquor through one-stage stripping with 0.5 mol/L hydrochloric acid solution. Infrared spectroscopic analysis and slope analysis revealed that the composition of the extracted complex was (C 8 H 17 C 6 H 4 OCH 2 COO) 3 Al, which was bound via hydrogen bonding with R 3 NH + produced from the reaction between N235 and H + . Na-saponified CA12 has a high extraction capacity for aluminum, with single-stage extraction efficiencies of 99% for aluminum, 6.7% for cobalt and 8.2% for nickel , but has difficulty in phase separation. CA12-N235 system has advantages of high extraction capacity for aluminum and quick phase separation compared with naphthenic acid and P507.

Preparation of Alnico magnet with high magnetization by thermal deformation

Fe-Co-rich α1 and Al-Ni-rich α2 ribbons were compounded by hot isostatic pressing and hot rolling in a ratio of 2:1, subsequently, the Alnico alloys were subjected to traditional heat treatment. This new composite method solved the problem of the uncontrollable ratio of α1 to α2 phase in Alnico alloy and can form a two-phase embedded microstructure, especially the saturation magnetization of the alloy can be significantly improved. However, the coercivity decreases due to the small aspect ratio of α1 phase and coarse phase size, this needs further improvement. Besides, the effects of temperature, pressure and magnetic field on the diffusion direction of elements are disclosed.

Comparison of sequential and circular scanning thermal fields and their influence on microstructure of Alnico alloy produced by laser powder bed fusion

Residual stress create deformations and stress in additive structures that lead to geometry deviations of created elements of 3D models and defects as pores and cracks that occur in construction process. Our work rests upon theoretical and experimental approach to the study. The main objective is to compare thermal fields with the microstructure of samples and to establish relationship between laser powder bed fusion (LPBF) modes and the structure of the samples to be created. 3D finite element method (FEM) is used for macroscopic modeling to assess the effect of thermal fields on the microstructure of Alnico alloy. Comparison of the temperature fields with the microstructure of samples made by LPBF showed that the type of scanning (both bidirectional and circular) had a strong influence on the distribution of the thermal fields and, accordingly, on the microstructure of the samples made by LPBF.

Structure and magnetic properties of alnico alloy doped SmCo5–xCux ribbons

Multicomponent doping may be a promising way to optimize the composition of SmCo5-based alloys. Moreover, the magnetic properties of Sm-Co alloys are particularly sensitive to Cu. In this paper, the effect of Cu content and annealing process on the structure and magnetic properties of Alnico alloy doped SmCo5–xCux ribbons was studied. It was found that Cu addition refines the grains, expands the difference in Cu concentration of Sm- and M-rich (M = Al, Ni, Fe, Cu) Sm(Co, M)5 grains, promotes the solute and phase separation, and increases both coercivity and magnetization of the x ≤ 3 as-spun ribbons. The x = 0.3 as-spun ribbons exhibit excellent magnetic properties of Hc = 24.6 kOe, Mr = 55.9 emu/g, and M9T = 69.1 emu/g. Annealing at 600 °C for 30 min further improves the Hc to 30.1 kOe but decreases the Mr and M9T to Mr = 41.6 emu/g and M9T = 54.2 emu/g, respectively. The formation of the lamellar or granular Sm2(Co, M)7 grain boundary phase and ordered Sm(Co, M)5 grains may play important roles in improving the coercivity of the annealed ribbons.

An exploration of nanocomposite Nd-Fe-B/Alnico alloys with enhanced intergrain interactions and improved magnetic properties

Nd-Fe-B alloys have high intrinsic coercivity, high magnetic energy density, but low Curie temperature and poor temperature stability. While Alnico alloys have high Curie temperature and high temperature stability, but low intrinsic coercivity and low magnetic energy density. It would be of great scientific, technological and economical interest if these two alloys could be combined together in some proportion to make composite magnets with good comprehensive properties. Here we report nanocrystalline composite magnets containing Nd-Fe-B hard phase and alnico semi-hard phase fabricated by melt-spinning technique. A novel core-shell like structure constituting Nd-Fe-B (2:14:1) phase as core and Alnico rich phase as shell was obtained by optimizing the composition and processing conditions. The maximum energy density was enhanced upto 150 kJ/m3 in nanocomposite magnets. The Curie temperature of the main phase increased to 654 K for Nd-Fe-B/Alnico from 581 K for pure Nd-Fe-B alloy, which is attributed to the molecular field penetration of Alnico phase into the hard 2:14:1 phase, in addition to the substitution of Fe by Co and Ni. No kink or dip was observed in the demagnetization curves, which suggested the presence of strong exchange interactions among the phases of the nanocomposite alloys.

Tailoring the microstructure, magnetic properties and interaction mechanisms of Alnico-Ta alloys by magnetic field treatment

Reducing the spatial dimensions of spinodally decomposed phases and enhancing their magnetization difference is a promising route for enhancing the magnetic properties of Alnico alloys. In this paper we report the effects of various heat treatments on the formation of spinodal phases and magnetic properties of Alnico cast alloys. After optimizing the heat treatment conditions, small amount of refractory element Ta is introduced into the alloys and the effect of Ta on the formation and purity of spinodal phases, magnetic properties and phase transition temperatures are investigated. The addition of Ta element improved the intrinsic coercivity (Hcj) of the alloys from 1.52 kOe for standard alloy to 1.83 kOe for 0.6% Ta, while the remanence (Jr) remained nearly unchanged. Scanning electron microscopy analysis confirmed the rod-like Fe–Co rich (α1) phase embedded in Al–Ni–Cu–Ti rich matrix phase. A volume fraction of higher than 67% is obtained for α1 phase, while an ameliorating effect of γ-phase suppression at grain boundaries and triple junctions was noted. The alloy with optimized composition possessed extraordinary thermal stability in the temperature range 300–800 K, which is attributed to the shape anisotropy and uniformly distributed nano mosaic structure. Finally, the interaction mechanisms in Alnico alloys were investigated by means of Henkel plot and the motor applicability was analyzed by recoil loops.

Evolution of Microstructure, Magnetic Properties, and Thermal Stabilities of Isotropic Alnico Ribbons

The magnetic properties of alnico alloys are highly dependent on the spinodally decomposed nanostructure. In this article, we report the fabrication of alnico nanoribbons and the effects of various heat treatments on the magnetic properties, spinodal decomposition, microstructure, and temperature stability. It is found that the spinodal decomposition occurs in a wider range of temperatures from 800 °C to 860 °C. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses of the microstructure confirmed that the nanostructure phases develop in a wide temperature range. Aspect ratio of the order of ~20 is obtained by optimizing the heat treatment conditions. Magnetic properties of H cj = 815 Oe, B r = 6.70 kG, and (BH) max = 1.88 MGOe are obtained after simplified heat treatment. The magnetic properties of the alloys are measured at low (10 K) and at high (800 K) temperature, and it is shown by calculating temperature coefficient of remanence (α) and temperature coefficient of coercivity (β) that alnico ribbons possess extraordinary temperature stability at low and high temperatures.

Superhydrophobic and superhydrophilic properties of laser-ablated plane and curved surfaces

We examine the hydrophobic and hydrophilic properties of the plane and curved surfaces of different materials ablated using 5 ns laser pulses in air. The difference in the contact angles between liquid and surface of the modified graphite and AlNiCo alloy rods using different fluencies of the ablating pulses are demonstrated. The wetting contact angle of ablated graphite rod was found to be 147°, i.e., the modified curved surfaces demonstrated the superhydrophobic properties. On the other hand, the superhydrophilic properties, with 7° wetting contact angle, were demonstrated in the case of ablated aluminum alloy. A schematic model was proposed for the application of the graphite rod as a membrane for the oil–water separation.

Excellent magnetic properties determined by spinodal decomposition structure of Alnico alloy doped SmCo5-based ribbons

5 wt% Alnico5 doped Sm(Co0.9Cu0.1)5 ribbons were prepared by melt spinning at 40 m/s, and the effects of magnetic field heat treatment (MHT) and annealing on the phase composition, microstructure and magnetic properties of the ribbons were investigated. The results show that all three ribbons consist of Co-rich SmCo5-and Sm-rich CeCo5-type phases with a spinodal structure. Annealing increases the content of SmCo5-type phase, enlarges the component differences between the two types of Sm(Co,M)5 phases and accumulates Alnico alloying elements into 3 g site of CeCo5-type phase. MHT narrows the ingredient differences between them, prompting the Alnico alloying elements to diffuse simultaneously into 2c and 3 g sites of two Sm(Co,M)5 phases, and concentrates the CeCo5-type phase on grain boundaries of the SmCo5-type phase to pin the magnetic domain movement. The as-spun ribbons present the magnetic properties of Hc = 32.0 kOe, Mr = 46.2 emu/g and Ms = 59.1 emu/g, while MHT increases them by 10.0%, 10.2% and 19.5%, respectively. These results can contribute to disclose the multi-element doping mechanism for improving the magnetic properties of SmCo5-based or similar alloys.