3D characteristics and growth behavior of Fe-rich phases in Al-Si-Fe-Mn alloys during melt holding
(1. Guangdong Provincial Key Laboratory of Metal Toughening Technology and Application, Institute of New Materials, Guangdong Academy of Sciences, Guangzhou 510650, China;
2. National Engineering Research Center of Near-net-shape Forming for Metallic Materials, South China University of Technology, Guangzhou 510641, China;
3. School of Mechanical Engineering, Dongguan University of Technology, Dongguan 523808, China;
4. College of Materials and Metallurgy, Guizhou University, Guiyang 550025, China;
5. Jiangxi Universal New Material Technology Co., Ltd., Shangrao 334499, China)
2. National Engineering Research Center of Near-net-shape Forming for Metallic Materials, South China University of Technology, Guangzhou 510641, China;
3. School of Mechanical Engineering, Dongguan University of Technology, Dongguan 523808, China;
4. College of Materials and Metallurgy, Guizhou University, Guiyang 550025, China;
5. Jiangxi Universal New Material Technology Co., Ltd., Shangrao 334499, China)
Abstract: The morphological evolution and growth behavior 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 coarse star-like and polygonal structures to fine 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 structure was composed of polyhedrons and dendrites; 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 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.
Key words: holding temperature; Al-Si alloy; Fe-rich phase; 3D morphological evolution; synchrotron X-ray