Electromagnetic Vibration Process Research Articles

Effect of the simultaneous application of a high static magnetic field and a low alternating current on grain structure and grain boundary of pure aluminum

Effect of the simultaneous application of a high static magnetic field and a low alternating electric current on the solidification structure of pure aluminum has been investigated. Results show that the refinement of the solidification structure is enhanced by the electric current under a certain magnetic field. However, when the magnetic field intensity exceeds a certain value, the refinement is impaired under a certain electric current. The observation by electron backscattered diffraction (EBSD) shows the complex fields have led to the increase of the low angle boundaries with the refinement. Moreover, the application of the static gradient magnetic field is capable of modifying the distribution of the refined grains. The above results may be attributed to the formation of the cavities during the electromagnetic vibration process and the high magnetic field.

Creation of Fine Structure in Magnesium Alloys by Electromagnetic Vibration Process

We have developed the refinement process of the microstructure of metallic materials by imposition of electromagnetic vibration force during solidification. This process is effective for both wrought magnesium alloys and cast ones. By simultaneous imposition of a static magnetic field of 10 Tesla under an alternative electric current of 60A, the average grain sizes of the AZ31B wrought alloy and the AZ91D cast alloy were obtained about 50 micron in both alloys. The grain size was affected by electric current frequency and had the minimum value at the special electric current frequncy of 500 to 2000 Hz and 900 Hz for wrought alloy and cast alloy, respectively. From experimental results, we suggested the mechanism of refinement of microstructure during solidification by imposition of electromagnetic vibration force. The cavitation phenomenon in liquid phase during electromagnetic vibration was effective to break down th esolid phase. And also the difference of electric conductivity between the solid phase and the liquid one brought vigorous vibration of the solid phase. Then the solid phase was suppressed its growth.

Effects of magnetic field and electric current on the solidification of AZ91D magnesium alloys using an electromagnetic vibration technique

Using an electromagnetic vibration (EMV) technique, we solidified the AZ91D magnesium alloys at different magnetic flux densities and electric current levels when the vibration frequency was kept at 900 Hz so as to find the optimum processing parameters. The microstructure and microtexture of the alloy were examined under various magnetic fields, revealing that with the increase of the magnetic flux density, B 0, the microstructure becomes finer and finer and eventually consists of equiaxed grains with the average diameter approximately 57 μm at the magnetic flux intensity of B 0 = 10 tesla (T). In terms of the effect of the electric current on microstructure formation, the average grain size first decreases when the effective electric current, J e, increases from 10 to 60 ampere (A) and then increases when the electric current is further increased from 80 to 120 A. The grain refinement mechanism is clarified when considering the overall EMV process during solidification. The competition between the Lorentz force due to the imposition of the alternating current and the static magnetic force is also incorporated, which is of great importance in elucidating the microstructure and the microtexture formation.

Phase distribution and phase structure control through a high gradient magnetic field during the solidification process

Influence of a high gradient magnetic field on the phase distribution and phase structure has been investigated experimentally. It was found that the application of a gradient magnetic field is capable of controlling the distribution of the primary phase in alloys. As a consequence, an axial gradient magnetic field causes the primary MnBi phase in Bi–6wt.%Mn alloy and the primary Si phase in Al–18wt.%Si alloy to segregate from the matrix; and the application of a radial gradient magnetic field produces a ring-like MnBi phase-rich layer. The application of an axial gradient magnetic field can produce the even refining structure during the electromagnetic vibration process of pure Al through restraining the formation of crystal rains. The gradient magnetic field also affects microstructure by aligning the phase and controlling the phase aggregation process. Moreover, the investigation on the influence of an axial gradient magnetic field on the distribution of the element indicates that the field caused the Mn solute in Bi–6wt.%Mn alloy to separate from the Bi matrix.

Motion of Crystal Particles by the Electromagnetic Vibrations in Mg-Cu-Y Bulk Metallic Glasses

The method for producing Mg-Cu-Y and Fe-Co-B-Si-Nb bulk metallic glasses using electromagnetic vibrations is effective in forming the metallic glass phase. Disappearance or decrement of clusters by the electromagnetic vibrations applied to the liquid state is considered to cause suppression of crystal nucleation, because the electromagnetic vibrations vibrate the clusters vigorously in the melt. The purpose of this study was to investigate motion of the crystal particles by the electromagnetic vibrations in Mg-Cu-Y bulk metallic glasses. The electromagnetic vibration force vibrated the crystal particles or the clusters that become crystal nuclei in the melt, because the electric current for the electromagnetic vibrations concentrates in those. Thus, the electromagnetic vibrations were found to select vibration particles from the melt. Moreover, it was considered that composites for which second phases or other compounds are dispersed into the metallic glass phase or a nanostructure phase can be produced by the electromagnetic vibration process.

Effects of the simultaneous imposition of electromagnetic and magnetic forces on the solidification structure of pure Al and Al–4.5wt.%Cu alloy

Abstract Effects of the simultaneous imposition of an alternating current and a static magnetic field on the solidification structures of the pure Al and the Al–4.5 wt.%Cu alloy were investigated. The results show that the refined structure was gained by the application of the above complex fields. Owing to the fall of the refined nucleation during the electromagnetic vibration process (i.e. the formation of crystal rains), the refined structure was normally gained only at the bottom region of the sample. A method was proposed to restrain crystal rains by using an upward magnetic force and the results indicated that by using this method, the distribution of the refined grains was changed significantly. It was found that there existed a right magnetic force to make the whole sample refined; as a consequence, the uniformly refined structure was gained. In the case of the completely eliminating crystal rains, the effect of the electromagnetic force on the structure was investigated and result indicated that with the increase of the electromagnetic force density, the size of Al grains decreased and the depth of refinement zone increased. Moreover, the Al–4.5 wt.%Cu alloy was chosen to investigate the influence of the electromagnetic and magnetic forces on the growth of dendrite. It was observed that with the increase of the electromagnetic force density, the columnar dendritic structure changed into equiaxed ones that continued to disintegrate to isolated grains. Similar to the behavior of the pure Al, crystal rains formed during the electromagnetic vibration and could be restrained by using the magnetic force.

New Application of Electromagnetic Vibration Process for Creation of High Potential Metallic Materials

We have developed the new process for refinement of metallic materials during solidification without addition of refiners or without rapid cooling. This process uses electromagnetic body force based on the vibrations caused by simultaneous imposition of direct magnetic field and alternative electric current on the alloy melt during solidification. The vibrations create cavitation in the melt and it breaks out during growth of it. Then explosive force is released toward the surroundings such as the primary solid particles and they are fractured finely. Finally fractured solid particles solidified as very fine grains. This process was applied to hyper- and hypo-eutectic Al-Si alloys, and AZ91D Mg alloys. Primary silicon crystals in Al-17mass%Si alloy decreased the size remarkably by the optimum electromagnetic vibration condition. Primary aluminum dendrites particles in Al-7mass%Si and primary magnesium dendrite particles in AZ91D are also decreased its size markedly. This process has also been applied to create non-equilibrium state metallic materials such as metallic glasses. We have succeeded to obtain metallic glasses in Mg-Y-Cu alloy system and Fe-Co-Si-B-Nb alloy system. These alloys solidified as fully crystals in this cooling rate without electromagnetic vibrations. These glasses are bulky and are used as structural material.

Grain Refinement of Tough Pitch Copper by Electromagnetic Vibrations during Solidification

Electromagnetic vibrations, which are generated by simultaneous imposition of a static magnetic field and an alternating electric field, were applied to the refinement of crystal grains of tough pitch copper. The electromagnetic vibrations of the frequency range from 100 Hz to 10 kHz were imposed during solidification of the copper rod. Within this frequency range, the vibration frequency of about 100 Hz was found to be the most effective in refining the copper crystal grains and the average grain size was refined up to 200 μm, which otherwise was around 600 μm in a nonvibrated specimen. It was concluded that by the electromagnetic vibration process tough pitch copper could also be refined as well as Al-Si alloys and AZ91D alloys.

Electromagnetic vibration process for producing bulk metallic glasses

It is known that the cooling rate from the liquid state is an important factor in the production of bulk metallic glasses. However, the effects of other factors such as electric and magnetic fields have not been thoroughly investigated. Here, we present a new method for producing bulk metallic glasses by using electromagnetic vibrations with simultaneous imposition of an alternating electric current and a magnetic field. This method was found to be effective in enhancing apparent glass-forming ability in Mg65-Cu25-Y10 (atomic percent) alloys. Indeed, larger bulk metallic glasses could be obtained by the electromagnetic vibration process under the same cooling conditions. We presume that disappearance or decrement of clusters by the electromagnetic vibrations applied to the liquid state cause suppression of crystal nucleation. This electromagnetic vibration process should be effective in other bulk metallic glass systems if the clusters in the liquid state cause the crystal nucleation.

The Effect of Electromagnetic Vibration on the Silicon Size at Hypoeutectic Al-Si Alloy

In this study, the electromagnetic vibration process is adopted for modifying the eutectic Si phase and reducing its size. The higher the current density and frequency of electromagnetic vibration (EMV), the finer the size of the eutectic Si phase. The tensile strength and elongation of EMVed alloys were highly improved. Measured twin probability of EMVed alloy at a frequency of 1000Hz was approximately six times as high as that of the normal alloy and half of that of Sr modified alloy. The mechanism for the increase in twin density due to EMV during solidification could be suggested from the fact that the preferential growth along <112> in silicon was suppressed by preventing the Si atom from attaching to the growing interface of the Si phase and by changing the solid/liquid interfacial energy of silicon.

Effects of the Intensity and Frequency of Electromagnetic Vibrations on Glass-Forming Ability in Mg–Cu–Y Bulk Metallic Glasses

The present authors reported that a new method for producing Mg–Cu–Y bulk metallic glasses by using electromagnetic vibrations is effective in forming the metallic glass phase, and disappearance or decrement of clusters by the electromagnetic vibrations applied to a liquid state is presumed to cause suppression of crystal nucleation [Nature Materials 4 (2005) 289]. This paper aims to investigate the effects of the intensity and frequency of electromagnetic vibrations on apparent glass-forming ability in the Mg–Cu–Y bulk metallic glasses. It was found that the apparent glass-forming ability of Mg65Cu25Y10 alloys increases with increasing the frequency of electromagnetic vibrations up to 5000 Hz. The effects of frequency more than 5000 Hz could not be investigated because of alternating current power devices. Moreover, it was found that the apparent glass-forming ability of Mg65Cu25Y10 alloys increases with increasing the intensity of electromagnetic vibrations by an electric current or a magnetic flux density. However, increasing excessively the electric current was found to weaken the enhancement of the apparent glass-forming ability by using the electromagnetic vibration process because the crystalline particles grow larger by the Joule heat.