Arnold Rónaföldi

Effect of High Rotating Magnetic Field on the Solidified Structure of Al–7wt.%Si–1wt.%Fe Alloy

Al–7wt.-% Si–1wt.-% Fe alloy was solidified unidirectionally in the Crystallizer with High Rotating Magnetic Field (CHRMF). The diameter of sample was 8 mm and its length was 120 mm. The parameters of solidification were as follows: solid/liquid interface velocity ~0.082 mm/s, temperature gradient 7+/-1 K/mm, magnetic induction 0 and 150 mT, frequency of magnetic field 0 and 50 Hz. The structure solidified without rotating magnetic field (RMF) showed a homogeneous, columnar dendritic one. The structure solidified by using magnetic stirring showed a dual periodicity. On the one hand, the branches of the “Christmas tree”-like structure known from the earlier experiments contained Al+Si binary eutectic. On the other hand, bands with higher Fe- and Si-content formed in the sample, which were at a larger distance from each other than the branches of the “Christmas tree” structure. The developed microstructure was analyzed by SEM with EDS. The average Si- and Fe-concentrations were measured on the longitudinal section at given places along the length of sample. Furthermore the Si- and the Fe-concentrations close to the bands and among the bands as well as the composition of the compound phases were determined.

The effect of rotating magnetic field on the solidified structure of Sn-Cd peritectic alloys

The peritectic alloys, such as some types of steel, Ni-Al, Fe-Ni, Ti-Al, Cu-Sn, are commercially important. In contrast to other types of alloys, many unique structures (e.g. banded or island ones) can form when peritectic alloys are directionally solidified under various solidification conditions. It can be observed in the course of the directional solidification experiments performed in a rotating magnetic field (RMF) that the melt flow has a significant effect on the solidified structure of Sn-Cd alloys. This effect was investigated experimentally for the case of Sn1.6 wt% Cd peritectic alloy. For this purpose, a Bridgman-type gradient furnace was equipped with an inductor, which generates a rotating magnetic field in order to induce a flow in the melt. As a result, the forced melt flow substantially changes the solidified cellular microstructure. The cell size and the volume fraction of the primary tin phase were measured by an image analyzer on the longitudinal polished sections along the entire length of the samples. The microstructure was investigated by scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS).

Visualisation of the melt flow under rotating magnetic field

Experiments were performed for visual observation and investigation of liquid Gallium flow at a temperature of 40oC in a rotating magnetic field. Two different measuring methods were developed to determine the revolution number of rotating melt. In both cases the frequency of magnetic induction was 50, 100 and 150 Hz and the values of magnetic induction could be changed between 0 and 70 mT. The magnetic Taylor number changed between 0 and 3.54x107 during the experiments.

Modelling of Al-7%wtSi-1wt%Fe Ternary Alloy: Application to Space Experiments with a Rotating Magnetic Field

Recently several experiments on directional solidification of Al-6.5wt.Si-0.93wt.%Fe (AlSi7Fe1) alloy were performed under terrestrial conditions and onboard the International Space Station (ISS) in the Materials Science Lab (MSL) with use of electromagnetic stirring and without it. Analysis of the samples showed that stirring with a rotating magnetic field lead to the accumulation of iron-rich intermetallics in the center of the sample and influenced the primary dendrite spacing while the secondary dendrite arm spacing were not affected. In the present paper the accumulation of the intermetallics b-Al5SiFe in the center of the samples due to RMF stirring is demonstrated numerically and the evolution of primary and secondary dendrite arm spacing is discussed.

Numerical Simulation of the RMF Stirring of Molten Ga-In Alloy Using RANS K-ε and LES Turbulence Models

A comparison of the results of RANS k-ε and LES turbulence models was done via the simulation of the electromagnetic stirring of liquid 75,5%Ga-24,5%In alloy (in a 10 mm diameter & 30 mm high crucible) using Ansys Fluent. Each velocity component, the distribution of eddies inside the melt and other flow parameters were compared respectively. The accuracy was checked with measured angular velocity data of A. Rónaföldi. The turbulent energy spectra were also produced to see the validity of the LES models.

Comparison of Measured and Numerically Simulated Angular Velocity of Magnetically Stirred Liquid Ga-ln Alloy

A measurement of the angular velocity/revolution number of magnetically stirred liquid gallium-indium alloy was realized with newly developed angular velocity measuring equipment. To get additional information about the flow of the melt, a numerical simulation model was performed with ANSYS FLUENT 13.0 with a single phase 2D k-ε turbulence solver. The aim was to reproduce the flow as accurate as possible, so the measured and computed angular velocity data was compared, to see if the system can be modeled fairly well.

The Experiences with a Travelling Magnetic Field (TMF) Stirrer

An experimental stirring unit (inductor) using travelling magnetic field was tested for developing a solidification facility equipped with a magnetic stirrer. The investigations were performed by using an Sn50Pb alloy at temperature of 230°C. In the course of the experiments, the magnetic pressure developing in the metallic melt, the flow velocity of melt and the loss of flow were investigated using the TMF inductor.

The influence of surface roughness of crucible's wall on the flow rate of melt stirred during solidification

In the course of the unidirectional solidification performed in a rotating magnetic field (RMF), it can be observed that the flows, developing in the metallic alloy, melting under the influence of the magnetic field, have a significant effect on the developing structure. In the references [1, 2], the values of induction and frequency of magnetic fields creating the stirring, as well as the geometrical sizes of solidified samples, are used as parameters in case of identical alloys. An exact comparison can only be made in this case if the melt flows are similar during the procedures. However, the intensity of flow developing in the melt is influenced, not only by the geometrical parameters of magnetic field and that of the solidified samples, but by other various parameters as well.

Unidirectional solidification of Sn- Pb alloys under forced melt flow

Cylindrical Sn-Pb alloy samples of different compositions (10, 20 and 30 wt.-% Pb) were prepared from high purity (4N) components. After metals have been melted, a rotating magnetic field (RMF) with an induction of 150 mT and a frequency of 50 Hz was switched on in order to homogenize the liquid. The electromagnetic field was generated by a 3-phase, 2-pole inductor. Just before the start of the solidification process, the magnetic field was switched off to achieve a microstructure free of melt flow influence. The sample translation velocity was constant (0.05 mm/s), and the temperature gradient changed from 7 to 3 K/mm during the solidification process. The first half part of each sample solidified without influence of rotating magnetic field while solidification of the second half part proceeded under the action of the RMF. The columnar microstructure formed in the absence of RMF induced fluid flow was replaced after switching on the RMF by a characteristic Christmas tree- like macro-segregated structure with equiaxed dendrites. The secondary dendrite arm spacing and the volume fraction of primary tin phase (dendrite) were measured by an automatic image analyzer on the longitudinal polished sections along the whole length of the samples. The effect of the forced melt flow and alloy composition on its micro- and macrostructure development was investigated.

Effect of the High Rotating Magnetic Field (min. 30 mT) on the Unidirectionally Solidified Structure of Al7Si0.6Mg Alloy

The topic of this paper is the unidirectional solidification of ternary Al7Si0.6Mg aluminium alloy in a rotating magnetic field of 30 -150 mT and the characterisation of effect of stirring on the solidified structure. During performing the experiment-series, one of the three solidification parameters (temperature gradient, solid/liquid interface velocity and magnetic induction) was continuously changed and the other two of them was kept on a constant value. The effect of these parameters on the developed structures was analysed during the evaluation of the experimental results. Moreover, the extent of Si-macrosegregation as well as the change of the secondary dendrite arm spacing were investigated on the longitudinal and cross-sections of samples as a function of the three basic parameters.