中国有色金属学报(英文版)
Transactions of Nonferrous Metals Society of China
| Vol. 10 No. 6 December 2000 |
（1. College of Materials Science and Engineering, Shandong University of Technology,
Ji′nan 250061, P.R.China;
2. Department of Applied Physics, Northwestern Polytechnical University, Xi′an 710072, P.R.China）
Abstract:The drop tube technique was performed to achieve rapid solidification of undercooled Al-18%Si hypereutectic alloy. The droplets ranging from 60~1000μm in diameter were obtained. The regular polygonal primary Si and lamellar eutectic homogeneously distribute onα(Al) matrix in the droplets larger than 500μm. While in the droplets smaller than 500μm the five-star primary Si was found, which is often accompanied by some spherical eutectic grains. The different morphologies of primary Si are due to varied undercoolings. Scanning electron microscopy suggests that the spherical eutectic grain is composed of anomalous eutectic in its core and lamellar eutectic radiating outside from its periphery. Such eutectic microstructure is presumed to be the result of combining large undercooling, microgravity with containerless processing during free fall.
Key words: rapid solidification; undercooling; Al-Si alloy; drop tube
