Search Results (6)

Hypereutectic Al-Si alloys containing primary Si exhibit unique material properties that make them suitable for various industrial applications. Understanding the characteristics of primary Si is crucial for predicting the effect of solidification conditions on the microstructure of these alloys. This paper presents a comprehensive characterisation study of primary Si in hypereutectic alloys. This study provides a detailed analysis of the size, distribution, and morphology of primary Si, providing valuable insights into the alloy structure, mechanical properties, and even the performance of the production process. The effect of forced melt flow by a rotating magnetic field (RMF) and solid/liquid front velocity on the size and morphology of primary Si in a hypereutectic Al-18 wt.% Si alloy was investigated. The purpose of using the RMF technique during the solidification process of Al-Si alloys is to enhance the alloy’s microstructure by inducing electromagnetic stirring. The hypereutectic samples were solidified at five different front velocities (0.02, 0.04, 0.08, 0.2, and 0.4 mm/s), under an average temperature gradient (G) of 8 K/mm, in a crystalliser equipped with an RMF inductor. Each sample was divided into two parts: the first solidified without stirring, while the second underwent electromagnetic stirring using RMF at an induction (B) of 7.2 mT. The results revealed that increasing the front velocity during solidification refined the primary Si in stirred and non-stirred parts. In non-stirred parts, it decreased dendritic forms and increased star-like Si, while polyhedral shapes remained nearly constant. Stirred parts showed stable Si morphology across velocities. Higher velocities also promoted equiaxed over elongated Si forms in both parts. Full article

The microstructure of hypereutectic Al-Si alloys is crucial in determining their mechanical properties and overall performance in engineering applications. This paper investigates the effect of a rotating magnetic field (RMF) and eutectic front velocity on the microstructure of hypereutectic Al-18 wt.% Si alloy. The hypereutectic samples were solidified using five different front velocities (0.02, 0.05, 0.09, 0.2, and 0.4 mm/s) with an average temperature gradient (G) of 8 K/mm in a crystallizer equipped with an RMF inductor. The samples were solidified into two sections. The first section solidified without stirring, while the second section solidified with stirring using RMF at an induction (B) of 7.2 mT. The length, angular orientation of eutectic Si lamellas, and interlamellar distances were measured in both the non-stirred and the stirred sections to evaluate the impact of RMF and front velocity on the eutectic structure. The results revealed that the application of RMF and the increase in front velocity during solidification led to the significant refinement of the eutectic structure. These findings highlight the potential of RMF and front velocity manipulation to enhance the microstructure of hypereutectic Al-Si alloys, with practical implications for the development of high-performance materials. Full article

The paper explores the characteristic indicators of the operation of a magnetic mill. A magnetic mill is a device designed for grinding or mixing substances by interaction with ferromagnetic working elements moving in a rotating magnetic field. The study established the main factors influencing force interaction between the components of such a system. An analysis of the magnetic field inside the working zone of the mill was conducted and the method of calculating the quantitative indicators of this interaction was found. The method responds to changes in the size of these elements, their position in the mill working area and changes in the intensity of the magnetic field. A mathematical model was developed. The model is used for calculating the trajectories of movement of the ferromagnetic elements that are placed in a rotating magnetic field and are confined by space of the working zone of the mill. Indicators directly related to the productivity of the grinding/mixing process were determined following an analysis of the simulation results. Based on comparison of the results obtained by calculation and experimental methods, it was proven that the proposed method is suitable for evaluating the productivity of the grinding/mixing process in a real technological system containing a magnetic mill. Full article

Using magnetic stirring during solidification provides a good opportunity to control the microstructure of alloys, thus controlling their physical properties. However, magnetic stirring is often accompanied by a change in local concentrations, and new structures form which could harm the physical properties. This research paper investigated the effect of forced melt flow by a rotating magnetic field (RMF) on the macrostructure of an Al-Si eutectic alloy. To serve this purpose, Al-12.6 wt% Si alloy samples were solidified in a vertical Bridgman-type furnace equipped with a rotating magnetic inductor to induce the flow in the melt. The diameter and length of the sample are 8 mm and 120 mm, respectively. The solidification parameters are a temperature gradient (G) of 6 K/m, and the solid/liquid front velocity (v) of 0.1 mm/s. These samples were divided into parts during the solidification process, where some of these parts are solidified under the effect of RMF stirring while others are solidified without stirring. The structure obtained after solidification showed a distinct impact of stirring by RMF; new phases have been solidified which were not originally present in the structure before stirring. Besides the eutectic structure, the new phases are the primary aluminum and the primary silicon. The Si concentration and the volume fraction of each phase were measured using Energy-Dispersive Spectroscope (EDS)and new image processing techniques. The experimental results reveal that applying the RMF during the solidification has a distinct effect on the macrostructure of Al-Si eutectic alloys. Indeed, the RMF provokes macro-segregation, reduces the amount of eutectic structure, and changes the sample’s Si concentration distribution. Full article

This article presents a new method of excitation for a fast-changing rotating magnetic field (RMF) of higher frequencies (HF) causing the hyperthermic effect in magnetic fluids. The method proposed here uses a magnetic field exciter (inductor) consisting of a ferrite magnetic circuit and a system of coils connected in a two-phase arrangement. The proposed system is powered by two higher-frequency rectangular signals, with a 90-degree phase shift between each other, through HF transformers with ferrite cores. This paper presents the outcomes of the operation of RMFs in the frequency range of 38 kHz to 190 kHz, with a value of amplitude of magnetic field intensity H equal to 20 kA/m and increasing temperature, in a sample of APG513 magnetic liquid. The obtained results show that, in the range of the magnetic field intensities of moderate values, at a constant frequency f, the values of the time derivative of temperature are proportional to the square of the magnetic field intensity dT/dt~H². Moreover, the values of the temperature rate, which are measured with the constant value of the magnetic field intensity, are proportional to the square of the frequency dT/dt~f². At higher amplitudes of the RMF, the relationship dT/dt~H² is no longer fulfilled, and an inflexion point of this function appears. In the case of the highest values of the achieved intensity amplitudes (H = 20 kA/m), the parameter of the Langevin function achieves a value equal to ξ = 6. Full article

Al–Si eutectic alloys are industrially important; they play a significant role in the casting-manufacturing of most materials. The properties of the materials are governed by their microstructure, which can be tuned by adjusting the solidification process parameters. Herein, the effect of forced melt flow on the microstructure of an Al–Si eutectic alloy during unidirectional solidification was investigated experimentally. Al–12.6-wt%-Si alloy samples were solidified in a vertical Bridgman-type furnace equipped with a rotating magnetic inductor to induce flow in the melt. The samples were subjected to different magnetic induction conditions during the solidification experiments. The diameter of the samples was 8 mm, and their length was 120 mm. The eutectic alloy samples were solidified unidirectionally at a growth rate of v ≈ 0.1 mm/s and a temperature gradient of G ≈ 6 K/mm. The inter-lamellar distances (λ), lengths, and orientation angles of the Si lamellae were investigated using new measurement methods. The experimental results reveal that applying the rotating magnetic field (RMF) during the solidification has a distinct effect on the microstructure of Al–Si eutectic alloys. Indeed, the RMF refines the eutectic structure, reduces the interlamellar distances, and increases the diversity of the Si lamella angle’s orientations. However, the successive stirring process has a negligible effect on the lengths and angles of Si lamellae. Full article