Low-voltage Pulsed Magnetic Field Research Articles

Influence of the low voltage pulsed magnetic field on the columnar-to-equiaxed transition during directional solidification of superalloy K4169

The low voltage pulsed magnetic field (LVPMF) disrupts the columnar dendrite growth, and the columnar-to-equiaxed transition (CET) occurs during the directional solidification of superalloy K4169. Within the pulse voltage ranging from 100 V to 200 V, a transition from columnar to equiaxed grain was observed, and the grain size decreased as the pulse voltage rised. As the pulse frequency increased, the CET occurred, and the grains were refined. However, the grains became coarse, and the solidification structure was columnar crystal again when frequency increased to 10 Hz. The LVPMF had an optimal frequency to promote CET. The LVPMF on the CET was affected by the withdrawal speed and increasing the withdrawal speed enhances the CET. The distribution of electromagnetic force and flow field in the melt under the LVPMF were modeled and simulated to reveal the CET mechanism. It is considered that the CET should be attributed to the coupling effects of magnetic vibration and melt convection induced by the LVPMF.

Numerical Simulation of Grain Refinement of Pure Copper Solidified under Pulsed Magnetic Field

Grain refinement of pure copper solidified with the low voltage pulsed magnetic field (LVPMF) has been achieved in our previous experiments. To further study the influence of solidification condition on the as-cast structure and the relevant mechanism, the numerical investigation of grain growth of pure copper under LVPMF was conducted in the present work. The calculation result indicates that the temperature field and the cooling rate in the melt of pure copper become more uniform for the condition with LVPMF, meanwhile the cooling rate of melt in central region is much higher than the case without LVPMF. It is found the grain refinement by LVPMF is strongly related to the cooling condition. For the case without LVPMF, the larger the cooling rate is, the smaller the arm spacing of columnar grain structure. Under the LVPMF, the solidification pattern changes to equiaxed grain structure and the better grain refinement can be achieved with lower cooling rate.

Influence of temperature conditions on grain refinement of pure Cu solidified with low-voltage pulsed magnetic field

The influence of temperature conditions on the grain refinement of pure Cu solidified with low-voltage pulsed magnetic field (LVPMF) was investigated. With the pouring temperature (Tp) and mould temperature (Tm) increasing, the solidified microstructure of pure Cu was gradually changed from fine equiaxed grains to coarse columnar grains and then to the mixed structure of coarse equiaxed grains and columnar grains. Little change was observed from the microstructure of pure Cu solidified with and without LVPMF for the low Tp and Tm. But for the high Tp and Tm, applying LVPFM remarkably reduced the coarse columnar grains and obtained fine equiaxed grains. The grain refinement by LVPFM is considered to be caused by the electromagnetic flow. The smaller cooling rate resulted by higher Tp and Tm offers much acting time for LVPMF and thus better grain refinement can be achieved.

As-cast structure and tensile properties of AZ80 magnesium alloy DC cast with low-voltage pulsed magnetic field

The effects of a low-voltage pulsed magnetic field on the solidified structure and mechanical properties of DC casting AZ80 magnesium alloy were investigated. The results showed that the solidified structure of the DC casting AZ80 magnesium alloy was refined obviously by the low-voltage pulsed magnetic field and significant grain refinement in the DC casting ingot of AZ80 magnesium alloy was achieved. Meanwhile, the morphology of the dentritic in the DC casting ingot was transformed from coarse dentritic to fine rosette with the application of low-voltage pulsed magnetic field. The ability of deformation of the ingot was enhanced and especially the plasticity of the ingot center after upsetting was improved greatly by more than 80% after deformation.

Grain refinement of as cast superalloy K4169 solidified with low voltage pulsed magnetic field

The solidification behaviour and the as cast structure of superalloy K4169 ingots solidified with a low voltage pulsed magnetic field (LVPMF) were investigated by experiments and modelling. The experimental results showed that complete fine equiaxed grains in ingots of diameter 95 mm were obtained by applying an LVPMF. Dendrite tips in the as cast structure were rounded due to the release of latent heat and the concentration of the Joule heating effect on the dendrite tips. The solidification procedure was simulated in order to investigate the grain refinement mechanism. The simulation results show that the LVPMF has electromagnetic convection and electromagnetic vibration effects on the alloy melt. Grain refinement was considered as the result of the magnetic force and melt flow during solidification. Based on the experimental and simulation results, a refining mechanism was proposed for nucleus multiplication by melt vibration and convection, which contributes to heterogeneous nucleation enhancement and leads to high nucleation rate and grain refinement.

Refinement mechanism of low voltage pulsed magnetic field on solidification structure of silicon steel

The grain refinement of a silicon steel solidified with a low voltage pulsed magnetic field (LVPMF) was investigated by experiments and modeling. The experiment results show that complete fine equiaxed grains are acquired by applying the LVPMF. The effects of process parameters, such as the melt cooling rate and superheating on the solidification structure, were also studied. Complete fine equiaxed grains can be obtained under a larger range of cooling rate or superheating when the LVPMF is applied. The magnetic force and the melt flow during solidification were modeled and simulated to reveal the grain refinement mechanism. The simulation results show that the LVPMF has a double role in electromagnetic convection and electromagnetic vibration on the alloy melt. We propose the refining mechanism: The melt vibration and convection can promote nucleus multiplication, which contributes to heterogeneous nucleation enhancement and leads to a high nucleation rate and grain refinement.

Grain Refinement of Superalloy K4169 with Low-Voltage Pulsed Magnetic Field Treatment

The influences of different pouring temperature and mold temperature on solidified structure of superalloy K4169 under low-voltage pulsed magnetic field (LVPMF) were investigated in the paper. The experimental results show that solidified structure of superalloy K4169 under LVPMF can be refined greatly with appropriate cooling rate of the alloy. The dendrite growth is restrained and the microstructure is changed from larger dendrite grains to smaller equiaxed grains. When the pouring temperature is at 1380 °C-1530 °C or the mold temperature is at 1000 °C-1300 °C, the increase of pouring temperature or mold temperature enhances the refinement effect of LVPMF processing. With the increase of the pouring temperature or the mold temperature, average grain size of the alloy decreases and the primary phase degrades from developed dendrites into equiaxed crystals under the LVPMF.

Effect of Low-Voltage Pulsed Magnetic Field on Solidified Structure of Superalloy K4169

Effects of different pulse voltage and frequency on solidified structure of superalloy K4169 under low-voltage pulsed magnetic field (LVPMF) were investigated in this paper, and the related mechanism was also discussed. The experimental results show that grain of superalloy K4169 can be refined greatly by LVPMF treatment during the course of solidification. Growth of dendrite is restrained and primary grain is changed from large dendrites to smaller equiaxed grains. When the pulse voltage is at 0-280V, grain size of the alloy decreases as pulse voltage increases, and primary dendrites are fractured from well-developed dendrites into fine equiaxed grains and non-dendritic structures. When the pulse frequency is at 0-5Hz, the increase of pulse frequency enhances the refinement effect of LVPMF processing. With the increase of the pulse frequency, grain size of the alloy increases.

Grain Refinement of 6061 Alloy by Low-Voltage Pulsed Magnetic Field Treatment

The influences of different pulse voltage and mold temperature on solidified structure of 6061 alloy under low-voltage pulsed magnetic field (LVPMF) were studied. The results show that grain of 6061 alloy can be refined greatly by LVPMF treatment. The dendrite growth is restrained and the microstructure is changed from larger dendrite grains to smaller nondendritic grains. When the pulse voltage is at 0V-300V, grain size of the alloy decreases as pulse voltage increases, and the primary phase degrades from developed dendrites into rose-like or spherical crystals. When the mold temperature is at 20°C-600°C, the decrease of mold temperature enhances the refinement effect of LVPMF processing. With the decrease of the mold temperature, grain size of the alloy decreases.

Effect of low voltage pulsed magnetic field on microstructure and wear behaviour of eutectic Al–Si alloys

Effect of discharging frequency of low voltage pulsed magnetic field (LVPMF) on the morphology and size of eutectic Si in eutectic Al–Si (Al–12Si) alloys has been investigated, and some characteristic parameters the characterised the microstructure of the eutectic Si phase were obtained. Dry sliding wear behaviour of eutectic Al–Si alloys without and with LVPMF treatment were also tested using a pin-on-disc wear testing machine, and scanning electron microscopy and energy dispersive spectroscopy X-ray of worn surfaces were carried out to determine the governing mechanisms in the eutectic Al–Si alloys without and with LVPMF treatment. The results show that the eutectic Si became smaller with the increase in discharging frequency. Fine short rod-like or rounded particle-like eutectic silicon with 2·3 μm in length, 0·6 μm in the width, and 3·8 in aspect ratio was formed in eutectic Al–Si alloy treated by 6 Hz LVPMF. The wear resistance of eutectic Al–Si alloys increased with the increase in discharging frequency. The adhesive wear was observed in eutectic Al–Si alloy without LVPMF treatment under normal load of 80 N. However, mainly abrasive was observed in eutectic Al–Si alloy with 6 Hz LVPMF treatment.

Grain refinement of Al–Cu alloy in low voltage pulsed magnetic field

The effect of a low voltage pulsed magnetic field (LVPMF) on grain refinement of Al–Cu alloy was investigated at different solidification stages. The cooling curve was also studied to investigate the grain refinement mechanism of LVPMF. The fine grains are obtained by applying the LVPMF during the nucleation stage. The LVPMF has no obvious influence on the solidification structure when it is applied during liquid phase stage or crystal growth stage. Application of LVPMF increases the nucleation temperature of the isomorphous transformation, and also decreases the recalescence magnitude of the alloy. The refining mechanism was proposed that the LVPMF provides extra energy for nucleation, which decreases the energy barrier and the critical radius for nucleation, leading to high nucleation rate and grain refinement.

Effects of Low-Voltage Pulsed Magnetic Field and Pouring Temperature on Solidified Structure of Al-4.5%Cu Alloy

The solidified structure refinement of Al-4.5%Cu under the action of low-voltage pulsed magnetic field (LVPMF) was investigated in the paper. The influences of different pulse voltage and pouring temperature on solidified structure of Al-4.5%Cu alloy were studied. The results show that solidified structure of Al-4.5%Cu alloy can be refined greatly by LVPMF processing. The dendrite growth is restrained and the microstructure is changed from larger dendrite grains to smaller nondendritic grains, and with certain parameters, the equiaxed, non-dendritic grains are gained in the alloy. With the increase of pulse voltage, grain size of the alloy decreases, and the primary phase degrades from developed dendrites into rose-like or spherical crystals. The decrease of pouring temperature enhances the refinement effect of LVPMF processing. With 150 V pulse magnetic field treatment, grain size of the alloy decreases, primary phase degrades and refines gradually with the decrease of pouring temperature.

Microstructure and mechanical properties of Mg–Al–Zn alloy under a low-voltage pulsed magnetic field

Effect of a low-voltage pulsed magnetic field on the solidified microstructure and mechanical properties of Mg–Al–Zn alloy has been investigated. When the low-voltage pulsed magnetic field is applied during solidification, the as-cast microstructure is significantly refined and α-Mg is modified from developed dendrite to fine rosette. This morphology modification is caused by the accumulation of Joule heat on the dendrite tip. The yield strength is improved with the application of the low-voltage pulsed magnetic field under normal casting and semi-continuous casting conditions. The ultimate tensile strength is decreased slightly under normal casting condition due to the occurrence of plenty of shrinkage under the low-voltage pulsed magnetic field. The shrinkages are removed and the yield strength and ultimate tensile strength are increased under semi-continuous casting condition with low-voltage pulsed magnetic field.

Formation of the solidified microstructure of Mg–Al–Zn alloy under a low-voltage pulsed magnetic field

Abstract

Grain refinement of as-cast superalloy IN718 under action of low voltage pulsed magnetic field

The grain refinement of superalloy IN718 under the action of low voltage pulsed magnetic field was investigated. The experimental results show that fine equiaxed grains are acquired under the action of low voltage pulsed magnetic field. The refinement effect of the pulsed magnetic field is affected by the melt cooling rate and superheating. The decrease of cooling rate and superheating enhance the refinement effect of the low voltage pulsed magnetic field. The magnetic force and the melt flow during solidification are modeled and simulated to reveal the grain refinement mechanism. It is considered that the melt convection caused by the pulsed magnetic field, as well as cooling rate and superheating contributes to the refinement of solidified grains.