External Longitudinal Magnetic Field Research Articles

Magnetic controlled arc welding technology: a review

PurposeThe purpose of this study is to optimize and improve conventional welding using EMF assisted technology. Current industrial production has put forward higher requirements for welding technology, so the optimization and improvement of traditional welding methods become urgent needs.Design/methodology/approachExternal magnetic field assisted welding is an emerging technology in recent years, acting in a non-contact manner on the welding. The action of electromagnetic forces on the arc plasma leads to significant changes in the arc behavior, which affects the droplet transfer and molten pool formation and ultimately improve the weld seam formation and joint quality.FindingsIn this paper, different types of external magnetic fields are analyzed and summarized, which mainly include external transverse magnetic field, external longitudinal magnetic field and external cusp magnetic field. The research progress of welding behavior under the effect of external magnetic field is described, including the effect of external magnetic field on arc morphology, droplet transfer and weld seam formation law.Originality/valueHowever, due to the extremely complex physical processes under the action of the external magnetic field, the mechanism of physical fields such as heat, force and electromagnetism in the welding has not been thoroughly analyzed, in-depth theoretical and numerical studies become urgent.

Mathematical modelling of the emission characteristics of a field electron cathode in a scanning electron microscope under biosampling conditions

Currently, the use of electron microscopes in medicine is developing intensively, including scanning electron microscopes (SEM), which are designed to solve a huge number of problems in various fields with a wide range of electron accelerating voltages and electron beam energies. The development of an SEM with certain emission characteristics, with a range of lower beam energies for the study of biological samples, is an urgent task because modifying the SEM to solve problems in medicine, for example, would make it possible to obtain higher-quality images of biospecimens for diagnostics and monitoring the effectiveness of therapy. To develop new SEMs with certain characteristics, it is proposed to conduct less expensive research using numerical methods based on mathematical models of processes in electron-optical SEM systems. In this regard, this work sets the task of determining the size and shape of the beam, the main emission characteristics of the field electron cathode (FEC) of the SEM, which is under the influence of the electric field that excites electron emission and the external longitudinal magnetic field by studying the movement of the outermost electron of the beam, taking into account the influence of space charge beam electrons, external magnetic field. In the model, the FEC is approximated by a paraboloid of rotation, and the concept of a boundary “outermost” electron is introduced, the trajectory of which determines the shape and size of the beam. The problem of calculating the emission characteristics along the trajectory of the outermost electron of a FEC is solved using a mathematical model that includes the following equations: motion of the “outermost” electron, Maxwell outside and inside the beam, continuity of the current density, Fowler-Nordheim equation. As a result, a system of 18 first-order ordinary differential equations was obtained, the numerical calculation of which using the 4th order Runge-Kutta method allows us to obtain the emission characteristics of the FEC. As a result, it is suggested that it would be feasible to modify SEMs for more effective use in the medical field, taking into account their increasing use in disease diagnosis and the possible improvement of image quality through the development of FEC SEMs with more suitable characteristics.

Исследование изменения геометрических параметров образцов, наплавленных методом GMAW при воздействии на электрическую дугу продольного магнитного поля

Introduction. The paper presents the results of research of additive manufacturing process by electric arc with axial feeding of steel filler wire in protective gas environment (GMAW technology) with additional influence of external longitudinal magnetic field on electric arc. Purpose of work: an experimental study of the effect of a longitudinal magnetic field during additive manufacturing by an electric arc with axial feed of filler wire made of structural steels in a protective gas environment on the change in the geometrical characteristics of the layers being surfaced. Research Methods. The manufacturing of specimens was carried out on a 5-axis additive machine based on a CNC machine. Surfacing was carried out in the following modes: voltage 17.5 V; current 55–65 A; wire diameter 1.2 mm; wire material Sv-08G2S; wire feed rate 2,267 mm/min; approximate roll diameter 3.0 mm; roll length 50 mm; number of wires per one roll 312.5 mm; number of layers when surfacing the wall 5; magnet operation mode: alternating current with frequency 50 Hz, voltage 30 V; measured magnetic induction 5.7 mTl; initial height of the magnet above the substrate 10 mm; electrode stickout 10 mm; shielding gas: welding mixture CO2-Ar; gas pressure (flow rate) 0.15 MPa. Results and discussion. The conducted experimental study showed that the effect of longitudinal magnetic field had a statistically significant effect on the change in the dimensions of the singular, namely an increase in the width of the layers being surfaced by 34.1 %, with a calculated significance index close to zero, and a decrease in height by 20.2 %, with a calculated significance index equal to 2.7105. The effect of longitudinal magnetic field had a statistically significant effect on the change of the overall dimensions of the specimens consisting of five layers, namely, the width of the specimens increased by 11.2 % with a calculated significance index of 4.3103, and the height of the specimens decreased by 10.3 % with a calculated significance index of 6.3105. The effect of longitudinal magnetic field had no statistically significant effect on the change of the vertical deviation from straightness for the side walls of the specimens, with a calculated significance index of 0.3277, and had no statistically significant effect on the change of the error of the width of the walls of the specimens, with a significance index of 0.098.

Enhancing wire arc additive manufacturing in vibrational environments with longitudinal magnetic fields

To enhance the appearance and mechanical properties of Wire Arc Additive Manufacturing (WAAM) specimens within a vibrational environment, this study systematically investigated the forming process and results of ER50-6 steel deposition under external longitudinal magnetic field conditions. The research revealed that applying an appropriately longitudinal magnetic field significantly improved the appearance quality of the formed specimens, particularly under low vibration conditions, with optimized magnetic field parameters at a current of 0.95 A demonstrating prominent effects. The introduction of the longitudinal magnetic field effectively constrained the arc, imparting higher stability. Moreover, the magnetic field accelerated droplet transitions, reducing the occurrences of large droplets and short-circuit transitions, resulting in smoother droplet transitions. However, in high vibration environments, finding a magnetic field of suitable strength for substantial improvement proved challenging due to the influence of vibrational inertial forces. Finally, the introduction of the longitudinal magnetic field refined the grain structure and improved the tensile strength, yield strength and elongation of the samples, reaching 470 MPa, 358 MPa and 31.2%, respectively.

Numerical simulation of arc-droplet-weld pool behaviors during the external magnetic field-assisted MIG welding-brazing of aluminum to steel

The alternative longitudinal external magnetic field (LEMF) was verified to be effective to enhance the spreading and wetting capacity of the molten aluminum metal in metal inert gas (MIG) welding-brazing of aluminum to steel. This study proposed a three-dimensional arc plasma-molten aluminum-solid steel coupled model of LEMF-assisted MIG welding-brazing of aluminum to steel. The effect of LEMF on the arc plasma, metal transfer, weld pool behavior and temperature evolution at the brazing interface was analyzed. It was found that the alternative LEMF caused the periodical swinging of the arc plasma along the weld width direction and increased the velocity of the arc plasma under the undetached filler metal. The droplet velocity was decreased due to the deflection of the arc plasma force and the additional electromagnetic force. The periodical inclination of the droplet and arc plasma increased the lateral flow velocity of the molten aluminum metal so the spreading ability of the liquid aluminum on the surface of steel was improved. The heating area at the brazing interface between the molten aluminum and solid steel was expanded to improve the wetting of the molten metal. Besides, the peak temperature at the brazing interface decreased, which may suppress the growth of the intermetallic compound.

Study of the evolution of pulsed plasma under an external longitudinal magnetic field

An experimental study on the role of an external longitudinal magnetic field on the characteristics changes of pulsed plasma stream, produced in argon medium, is carried out at different time spans of its evolution. The spectroscopic observations are time integrated and are carried out at different times of plasma formation for pulsed discharge. This study gives insights into the recombination and diffusion phase of the plasma species in the presence of the magnetic field. The transition of plasma species from a dominant recombination phase to a diffusional phase is well revealed by the density profile during the time evolution. Moreover, the decrease in electron temperature and the increase in electron excitation temperature explain the energy transfer to electrons due to metastable quenching, and the system gradually approaches equilibrium. The magnetic field also affects the transitions of the ionized argon population between different energy levels. It is found that faster decay occurs for transitions of different plasma species to non-metastable states, while the populations of metastable states exist for a longer time. In addition, the time-resolved morphology changes of the plasma stream are also observed by high speed imaging, which shows the flow structure of the plasma stream at different time frames. The imaging of the plasma stream evolution shows the initial ejection of the plasma sheet from the electrode assembly, its detachment, the steady flow, and gradually its nature of dying out.

MI-Sensor Element Features and Estimation of Penetration Depth and Magnetic Permeability by Magnetoresistance and Magnetoreactance of CoFeSiB Amorphous Wires

The magnetoimpedance (MI) of amorphous soft magnetic Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">68.15</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4.35</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12.5</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sub> wires produced by the in-rotating water quenching technique was systematically studied. The behavior of the MI-element designed for magnetic sensors was examined in an external longitudinal dc magnetic field in the low-frequency range (f ≤ 1 MHz) and at the beginning of the intermediate frequency range (2 MHz ≤ f ≤ 5 MHz). A critical frequency of about 5 kHz - 7 kHz was observed with an initial increase in the MI effect. A maximum MI ratio of 334% was recorded at 0.95 MHz in a magnetically saturated MI-element. The intermediate frequency range is explored using the magnetoresistive - MR and magnetoreactive - MX components of magnetoimpedance Z. The MI anisotropy field profile occurs in the MHz operating frequency range with values increasing up to 25 A/m, exhibiting frequency dependence. The magnetic penetration depth was calculated using experimental magnetoresistance data, and the values obtained were about 3 μm - 4 μm for 5 MHz, showing a saturation trend. The magnetic permeability is analyzed in the framework of the electromagnetic classical high-limit model of a cylinder, which includes penetration depth and magnetoreactance. In our experiments and calculations, the classical high limit is satisfied in the operating frequency range of a few MHz. The magnetic permeability peak value is about 35% lower than the comparable data of amorphous CoFeNiMoSiB glass-coated microwires.

Linear and circular dichroisms of cholesteric liquid crystals in a longitudinal external magnetic field

ABSTRACT We investigated the properties of linear and circular dichroisms of cholesteric liquid crystal layer in external static magnetic field directed along helix axis. We showed that when the direction of light propagation and the direction of external magnetic field coincide, increasing the latter magnitude leads to a decrease in the linear dichroism, whereas when these directions are opposite, increasing the external magnetic field ( B e x t ) magnitude leads an increase in the linear dichroism. The presence of external magnetic field leads to the shift of circular dichroism curves both along wavelength axis and along dichroism axis. Then, we investigated the peculiarities of dichroism dependencies on B e x t for different wavelengths of incident light. We compared the dependence of circular dichroism on B e x t for a magnetically active cholesteric liquid crystal layer and an isotropic magnetically active layer and showed that while these dependencies are similar for wavelengths away from the photonic band gap, diffraction significantly affects these dependencies for wavelengths near and inside the photonic band gap. We investigated the evolution of spectra of linear and circular dichroisms at the change in B e x t , too. The results obtained can find application in the design of innovative polarised optoelectronic devices.

Effect of external longitudinal magnetic field on the dynamics of pulsed plasma stream

A spectroscopic study is carried out to investigate pulsed plasma stream produced in a coaxial plasma accelerator under the influence of an external longitudinal magnetic field. The dynamics of Argon plasma stream that includes the excitations and emissions of plasma species and its different parameter variations on the application of an external longitudinal magnetic field are reported in this work. The behavior of the ionized and neutral species of argon plasma is studied from their intensity distribution profiles which indicate the occurrence of faster recombination as compared to the field-free case. The variation of pressure reveals a significant influence on the recombination and diffusion process of the plasma species. Moreover, the variation of cathode voltage leads to variation in input energy to the system which influences the ionization and excitation processes of the plasma species. A plasma density (Ne) jump is achieved from 1021–1022 m−3 at a relatively higher pressure ∼8 bar plenum pressure in presence of the magnetic field. Saturation of the emissions and excitations of plasma species are revealed from the intensity profile and electron excitation temperature (Texc) profile which occur at different pressure and voltage both for field and field-free cases. The electron temperature (Te) is estimated using the FLYCHK code by comparing the simulated charge state distributions with the experimental findings. Using known parameters in the code, the different estimated Te shows a linear and an exponential decrement respectively in the absence and presence of the magnetic field. Maximum Te of 2.2 eV is reported which decreases to 1.51 eV at a significant increase of plasma density of 1022 m−3.

Short Circuiting Transfer, Formation, and Microstructure of Ti-6Al-4V Alloy by External Longitudinal Magnetic Field Hybrid Metal Inert Gas Welding Additive Manufacturing.

In this work, the external longitudinal magnetic field hybrid metal inert gas welding (M-MIG) additive manufacturing method is employed to produce the Ti-6Al-4V alloy part. The effect of process parameters on the droplet transfer formation and microstructure of the part was studied by a high-speed camera, optical microscope, and electron backscattered diffraction. The results showed that a typical short-circuiting transfer was obtained with the wire feeding speed of 2 m/min-4 m/min. An external longitudinal magnetic field had an obvious effect on the arc shape. The uniform formation of the deposition layer was obtained with the wire feeding speed of 4 m/min. The width of M-MIG deposition layer was greater than that of the MIG, and the width of M-MIG deposition layer was increased with the increase of the magnetic excitation current. The microstructure of the deposition layer was mainly comprised of acicular martensite α' and massive martensite αm. In addition, the β grain size in the M-MIG was less than that of the MIG. The average microhardness of the MIG deposition layer was 281.6 HV, which was less than that of M-MIG.

Microstructure Evolution of AZ91 Magnesium Alloy Welded Joint under Magnetic Field and NiCl2 Activated Flux

As the lightest engineering materials, magnesium alloys have been widely used. Because of the specific chemical and physical characteristics, the weldability of magnesium alloy is poor. Adopting suitable welding technology and improving the quality of magnesium alloy welded joints is key to their successful application. According to previous research data, it was found that the combined action of magnetic field and activated flux has a positive effect on improving-welding efficiency and improving the properties of a welded joint, butanalysis of microstructure evolution is insufficient. In this paper, AZ91 magnesium alloy was welded by TIG welding with activated flux and external longitudinal AC magnetic field. The phase composition and microstructure evolution were investigated. The experimental results revealed that the phase composition of welded joint was not changed due to the introduction of the magnetic field and activated flux, the growth patterns of grain in the weld seam and heat-affected zone were different. When the activated flux amount was 3 mg/cm2 with the effect of the magnetic field, the grain size of the weld seam was the finest, which was 18.96 μm. However, the grain size of the weld seam was larger than that of base metal. The crystallographic characteristics of grain boundaries in the weld seam and base metal were both LAGBs. The microstructure of the weld seam was messier than the base metal due to the larger misorientation angle. Under the combined action of the magnetic field and activated flux, the crystallization nucleation condition of the molten pool was changed, the formation of twins was promoted, and the crystal could selectively grow parallel with the (0001) basal plane.

Experimental investigations on the arc’s physical aspects and their implications on weld bead morphology and microstructure in TIG welding with an external longitudinal magnetic field

Experimental investigations on the arc’s physical aspects and their implications on weld bead morphology and microstructure in TIG welding with an external longitudinal magnetic field

The Feasibility Design Study and Cold Test of the First Model of HTS Cable With the Longitudinal Magnetic Field Effect

Since the 1970&#x2019;s the effect of the increase of the critical current of superconductors in the longitudinal external magnetic field has been known. The critical current density of a Nb-Ti wire at low longitudinal magnetic fields demonstrated several times the larger value compared with that in a transverse magnetic field. The same phenomenon has been observed for 2G HTS tapes. It is natural to try to use this phenomenon to increase the critical current in DC HTS power cables. In this paper, we present the analysis of feasibility to use the longitudinal magnetic field effect to increase critical currents in practical HTS power cables. The experimental model of the HTS DC cable has been developed, produced, and tested in liquid nitrogen. The increase of the critical current observed when the longitudinal magnetic field generated. This increase coincides with the calculations.

The magnetic properties of mixed spin-(52,12) anisotropic Heisenberg model in the Oguchi approximation

We have used the Oguchi approximation to study the effects of longitudinal crystal (D) and longitudinal external magnetic (h) fields on the mixed spin-(52,12) anisotropic Heisenberg model. The thermal variations of sublattice and total magnetizations are exploited in detail for given values of D, exchange anisotropy parameter (Δ) and coordination numbers z=3,4 and 6 when h=0.0. Thus, the phase diagrams are constructed on the planes of (D/J,kBT/J) and (Δ,kBT/J). In this case, it is found that the model presents either first- or second-order phase transitions as well as tricritical points. In the presence of magnetic field, the hysteresis loops of the model are also analyzed and it was found that the coercive field and remanent magnetization decrease as the temperature increases and increase as the crystal field or the exchange anisotropy increases.

Monte Carlo study of site disordered [formula omitted] Heisenberg models in the presence of a magnetic field and a weak random anisotropy

We study the 3d Heisenberg site disordered model with and without weak random anisotropy D in the presence of a uniform external longitudinal magnetic field using Monte Carlo methods. The spin and the chirality correlation lengths are measured. We provide evidence that the ”mixed chiral” phase is a chiral glass at a finite temperature transition TCG>0, whereas the spin glass temperature transition is at TSG=0 for D=0. In the anisotropic case we find that the model exhibited a strong evidence the occurrence of finite temperature transitions in the both sectors the spin and the chirality. Our estimate of the spin and chirality correlation-length exponents are compatible with our previous values obtained for the same model without anisotropy and the 3d Heisenberg spin glass.

Magnetic field induced rotation of the polarization plane of hydroxyl radical free induction decay in the terahertz region

Effect of the external longitudinal magnetic field on the optical free induction decay (FID) of the hydroxyl radical was investigated in detail. The experiments were performed on a rotational transition of OH (2Π3/2(J = 5/2) ← 2Π3/2(J = 3/2) at 83.8 cm−1) using the terahertz free electron laser. The rotation of the plane of polarization of FID as a function of time after the excitation of the radical was measured for various magnetic fields. The effect of nonmonotonic rotation of FID polarization plane in magnetic field was experimentally discovered. Numerical simulation of FID of the hydroxyl radical in a magnetic field has been carried out.

Streamer self-focusing in an external longitudinal magnetic field.

The numerical simulation of the development of a streamer discharge in a gap with an external longitudinal magnetic field was used to demonstrate the self-focusing of such discharges. Self-focusing is caused by a sharp deceleration of the radial ionization wave due to a change in the electron energy distribution function, a decrease in the average electron energy, the rate of gas ionization, and the electron mobility in crossed electric and magnetic fields as compared to the case of the discharge development without a magnetic field. The self-focusing effect of a streamer discharge in an external longitudinal magnetic field is observed for both positive and negative pulse polarities. The paper proposes an estimate of the critical value of the magnetic field, which makes it possible to control the development of pulsed high-voltage discharges at various gas pressures.

Phase diagrams and hysteresis behavior of the mixed spin-7/2 and spin-1/2 Ising model

The mixed spin-7/2 and spin-1/2 Ising model with a crystal field in the absence and presence of an external longitudinal magnetic field is investigated within the framework both of the renormalization group (RG) method and Monte Carlo simulation (MCS). First, we have determined the ground-state phase diagram. Then, using RG technique, the finite temperature phase diagrams of this model are plotted for the two- and three-dimensional cases by following the flow in the parameters space of the Hamiltonian and evaluating the free energy and its isotherm derivative at low temperatures. Our results show that the model exhibits first- and second-order phase transitions as well as critical end-points. In addition, by linearizing the RG transformation at the vicinity of the fixed points of the second-order transition, we have determined the critical exponents. The MCS is also employed to validate the results obtained previously by renormalization, and to examine the influence of an external magnetic field on the magnetic properties and hysteresis loops of the system.

Magnetic and thermodynamic behaviors of a diluted Ising nanographene monolayer under the longitudinal magnetic field

By means of Monte Carlo simulation, we have explored the magnetic and thermodynamic behaviors of the diluted ferromagnetic spin-3/2 Ising nano-graphene monolayer under the longitudinal magnetic field. The effects of the number of lattice sites, magnetic atom concentration, crystal field and external longitudinal magnetic field on the magnetic phase transition and hysteresis behaviors of the present system have been discussed. The characteristic curves of magnetization, magnetic susceptibility, internal energy and the specific heat as a function of temperature have been displayed specifically. We have presented the phase diagrams for various physical parameters. It is found that the area, coercivity and remanence of the hysteresis loops are strongly dependent on those selected parameters.

Magnetic Resonance Force Spectroscopy of Magnetic Vortex Oscillations

Forced oscillations of magnetization of NiFe circular disk in the presence of external longitudinal magnetic field are studied with the aid of micromagnetic simulation and experiments using magnetic resonance force spectroscopy. Main attention is paid to low-frequency resonance related to gyrotropic motion of the core of magnetic vortex. The resonance frequency of the gyromode is significantly shifted when the external magnetic field is applied in the sample plane. Effect of nonuniform magnetic field of the probe on the oscillations of magnetization is discussed.