Structural refinement of gray iron by electromagnetic vibrations

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.