Structural refinement of gray iron by electromagnetic vibrations |
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Authors: | Alireza Radjai Kenji Miwa |
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Affiliation: | (1) the National Institute of Advanced Industrial Science and Technology, Moriyama-ku, 463-8560 Nagoya, Japan |
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Abstract: | Simultaneous imposition of alternating electric and stationary magnetic fields on a molten metal will induce a vibrating motion
in the liquid, which can lead to the formation and collapse of cavities and affect the solidification structure. Following
earlier works on Al-Si alloys, the process is used to refine the microstructure of gray iron. It is found that in addition
to the refinement of columnar-dendritic structure of primary austenite into a fine and homogeneous one, the eutectic cell
structure is also extensively refined. The effects of the two main parameters involved in the process, that is, the frequency
and the intensity of vibrations are, for the first time, quantitatively presented. The refinement of the cells proceeds as
the frequency is increased up to about 500 Hz, where a reverse trend starts and results in a complete termination of the effects
at about 10 kHz. The increase in the number of cells because of the increase in the intensity of vibrations shows a sharp
jump at an electromagnetic pressure of about 105 Pa, where the cavitation phenomenon is more likely to occur by overcoming the static pressure. However, increasing the electromagnetic
pressure to higher values does not essentially result in a considerable further refinement, implicating the existence of a
limit in the process of structural refinement by the cavitation phenomenon. |
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