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摘要
The morphological evolution and growth of Fe-rich phases in the Al-7.0Si-1.0Fe-1.2Mn alloy during melt holding were studied using scanning/transmission electron microscopy， thermodynamic calculations and synchrotron X-ray imaging. The results show that with a decrease in holding temperature， the Fe-rich phase underwent a morphological transformation from star-like and polygonal to Chinese-script and coupled structures consisting of Chinese-script and polygonal shapes. The 3D structure of the star-like phase was composed of multibranched primary phases and irregular secondary phases; the coupled phase was composed of polyhedrons and dendrites; and the Chinese-script phase was composed of dendrites. When the holding temperature was decreased， the number and volume fraction of Fe-rich phases were significantly reduced. A similar trend was also obtained for the largest volume particles and their connectivity. In situ synchrotron X-ray radiography results indicated that these two types of primary Fe-rich phases were formed during the solidification process， and the smaller phase that remained in the melt could act as nucleation sites for the formation of the coupled eutectic structures.
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