Papers by Keyword: Pulsed Magnetic Field

Abstract: The transient electromagnetic phenomena and solidification of Al-Cu alloy under a typical pulsed magnetic field (PMF) are numerically studied by a two-dimensional (2D) axisymmetric model. The results show that the magnetic flux density, eddy current density, Lorentz force and Joule heat all inherit the instantaneous and intermittent feature of the PMF, and their amplitudes and phases decrease with the increasing distance to the side surface of the ingot. The Lorentz force appears alternatively as pressure force and pull force mainly in the radial direction. Forced convection is induced in the liquid metal, and the flow field is composed of a clockwise vortex and a counter-clockwise vortex in the meridian plane of the ingot. The melt velocity is accompanied with a dramatic periodic oscillation. The temperature field in the ingot with the PMF tends uniform due to the mixing effect of the melt flow. However, the convection is damped soon after the solidification starts due to the increasing penetration resistance, and the temperature field gradually approximates that in the case without the PMF.

Abstract: The aim of this investigation is to provide theoretical justification of the crystallizing nucleus formation in liquid iron. To solve this problem, the authors put forward the fluctuation hypothesis: short range order region formation in liquid metal takes place due to temperature fluctuations, and the temperature of the short range order is the temperature fluctuation around Kelvin scale zero in the course of crystallization time. The investigations were carried out for liquid state of the substance, in particular, for iron in paramagnetic state at the melting temperature. Analytical derivation of the temperature fluctuation value was given. Analytical expressions were obtained to define the average number of atoms in the short range order region for crystallizing iron. The investigation results show that short range order contains enough atoms to provide interaction with pulsed magnetic field resulting in the increase in the number of crystallization nuclei and in the decrease of their size. The obtained results can be used in the decision-making process concerning some manufacturing operations aimed at providing homogeneous structure of metals, particularly, in ferrous and non-ferrous metallurgy.

Abstract: The impact of a pulsed magnetic field on Sn diffusion in α-Fe is investigated within the magnetic field intensity range of 79.6–398.0 kА/m and the frequency range of 1–21 Hz at 730, 740, and 750 °С. The solute diffusion coefficients were measured by X-ray diffraction analysis. The pulsed magnetic field was found to influence significantly the diffusion coefficients of Sn in α-Fe. A resonant maximum of the bulk diffusion coefficient is observed at the frequency of 13 Hz and the magnetic field intensity of 398.0 kА/m. Possible mechanisms of the established magneto-diffusion coupling are discussed.

Abstract: In rail-gun launchers, the main current is pulsed and can reach up to several MA. The width of the pulse is about 2 - 4ms. When pulsed currents are supplied from the pulse power, it will generate a large transient magnetic field around the armature. Meanwhile, the armature will be accelerated up to 2km/s by a large electromagnetic force. In order to research the features of the fields around contact surfaces between rails and the armature, it needs to use a small-sized and battery-supplied data acquisition system to measure pulsed magnetic fields. The B-dot probe acts as a sensor to acquire the transient magnetic fields. All data will be stored in a SD card. The armature and SD card will be caught and fetched back after the launching. The system would be suitable and useful for the electromagnetic launcher design.

Abstract: The paper describes principles of construction of multi-block and multi-station pulse-magnetic installations. Main requirements for selection of elements of energy storages of installations with high stored energy and high frequency of the discharging current are presented. Examples of hardware implementation of the installations are shown.

Abstract: A brief review of experimental data on the effect exerted by both constant and pulse magnetic field upon the heterodiffusion in powders, polycrystalline and monocrystalline ferromagnetic metals and alloys is presented in the paper in order to analyze regularities and mechanisms of the initiation of numerous phenomena covered by the single term “magneto-diffusion effect”. The most probable mechanisms of the magnetic field influence on the diffusion processes are analyzed.

Abstract: The influences of pulsed magnetic field (PMF) on solidification structure of 6063 alloy were studied in this article. The results show that solidification structure of 6063 alloy can be refined with the application of PMF. The dendrite growth restrained and the macrostructure changed from large dendrite grains to fine equiaxed grains. The grain size decreased when the voltage increased from 0V to 600V. However, when the pulse frequency increased from 5Hz to 15Hz, the average grain size decreased continuously until reached a limit, and then the grains coarsened with further increase of the pulse frequency. The vibration caused by PMF not only made the temperature field of the melt uniform ,but also brook off the initial solidified grains formed on the cold wall of the mold, and spurs the grains to move to the center of melt which can be acted as nuclei.

Abstract: The influences of different pulse voltage, pulse frequency, pouring temperature and mold temperature on solidified structure of Mg₉₇Y₂Cu₁ alloy reinforced by long-period ordered structure with compound treatment of pulsed magnetic field and mechanical vibration were studied. The results show that grains of the alloy can be refined greatly with compound treatment. Primary phase degrades from developed dendrites into rosette-shaped crystal. Distribution of second phase is more uniform and continuous, and its volume fraction increases. When the pulse voltage is at 0-280V or the pulse frequency is at 1-10Hz, grain size of the alloy decreases dramatically as pulse voltage or pulse frequency increases. When the pouring temperature is at 660-750°C or the mold temperature is at 20-600 ^oC, grain size of the alloy with compound treatment decreases grossly with the increase of the pouring temperature or the mold temperature.

Abstract: Effect of pulsed magnetic field treatment on the microstructure and mechanical properties of Mg₉₇Y₂Zn₁ alloy has been investigated. When the pulsed magnetic field is applied on the alloy in semi-solid state, the α-Mg was modified from developed dendrite to fine rosette, resulting in a refined solidification microstructure with the grain size decreased from 4 mm to 0.5 mm. The volume fraction of the second phase ( X phase) increased by about 10 %. The yield strength, fracture strength and plasticity were improved by 21 MPa, 38 MPa and 2.4 %, respectively. The improvement of mechanical properties was attributed to the refined grain size and increased volume fraction of X phase.

Abstract: Magnetizations and optical Faraday effects have been intensitvely studied in transparent glasses of almost all Lanthanide elements with 20mol % in pulsed magnetic fields up to 30T in the temperature range between 1.8K-RT. The internal effective fields were investigated by observing Verdet constants as a function of applied fields and as a function of magnetizations in the wavelength range between 400nm and 2600nm, intensively for Nd, Pr , Tb and Dy glasses respectively. We obtained a magnet of Dy (30mol%) glass with optically transparent and adhesive to conventional magnet at the room temperature. The magnetizations of these glasses showed paramagnetism at the room temerature and showed super-paramagnetim at cryogenic temperatures below 4.2K.