Effects of the intensity and frequency of electromagnetic vibrations on the microstructural refinement of hypoeutectic Al-Si alloys
Effects of the intensity and frequency of electromagnetic vibrations on the microstructural refinement of hypoeutectic Al-Si alloys
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DOI：
10.1007/s11661-000-0017-2
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发表时间：
2000-03
期刊：
影响因子：
--
通讯作者：
A. Radjai;K. Miwa
中科院分区：
文献类型：
--
作者：
A. Radjai;K. Miwa
设计并组装了一种使用超导磁体的实验装置，该装置可以同时施加频率高达50千赫的交变电场和高达10 T的磁场。在两场同时作用下，al - 7wt - pct - Si合金在凝固过程中产生了电磁振动。在较宽的强度（电磁压力范围为0至2.25× 10.5 Pa）和频率（0至50 kHz）范围内进行了深入的研究，阐明了两个主要参数对电磁振动带来的微观结构细化的影响。低强度振动将高柱状枝晶结构转变为由大的等轴枝晶组成的结构。随着磁压力强度的增大，在0.93× 10 5 Pa左右，随着磁压力的进一步增大，开始出现细小的孤立晶粒并主导结构。在低频时，随着频率的增加，大的等轴枝晶分解成细小的均匀结构。在约1.5 kHz时，趋势逆转，在频率高于10 kHz时，结构逐渐变成完全柱状树突状结构。金相观察表明，空化现象是显微组织细化的主要原因。对实验装置的机械振动的影响也进行了研究，发现对观察到的效应没有贡献。
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× 10 5 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× 10 5 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.