Effects of the intensity and frequency of electromagnetic vibrations on the microstructural refinement of hypoeutectic Al-Si alloys |
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Authors: | Alireza Radjai Kenji Miwa |
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Affiliation: | (1) Japan Science and Technology Corp., the National Industrial Research Institute of Nagoya, AIST, MITI, Kita-ku, 462-8510 Nagoya, Japan;(2) the National Industrial Research Institute of Nagoya, AIST, MITI, Kita-ku, 462-8510 Nagoya, Japan |
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Abstract: | An experimental apparatus that uses a superconducting magnet and enables the simultaneous application of an alternating electric
field with a frequency of up to 50 kHz and a magnetic field of up to 10 T was designed and assembled. Electromagnetic vibrations
were induced in Al-7 wt pct Si alloy during solidification by simultaneous application of the two fields. The thorough investigation,
which was carried out over wide ranges of intensity (an electromagnetic pressure range of 0 to 2.25×105 Pa) and frequency (0 to 50 kHz), clarified the effects of the two main parameters on the microstructural refinement brought
about by electromagnetic vibrations. Low-intensity vibrations changed the highly columnar dendritic structure into one composed
of large, equiaxed dendrites. As the intensity, and consequently, the magnetic pressure were increased, at about 0.93×105 Pa, fine isolated grains started to appear and dominated the structure as the pressure was increased further. At low frequencies,
the structure was one with large, equiaxed dendrites, which disintegrated to form a fine and homogeneous structure as the
frequency was increased. At about 1.5 kHz, the trend reversed and the structure gradually became a completely columnar dendritic
one at frequencies higher than 10 kHz. Metallographic observations showed that the cavitation phenomenon has been a main factor
behind the observed microstructural refinement. The effects of mechanical vibrations of the experimental apparatus were also
investigated and found to have no contribution to the observed effects. |
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