中国有色金属学报(英文版)
Transactions of Nonferrous Metals Society of China
| Vol. 15 No. 3 June 2005 |
（1. Department of Mechanical Engineering, Shandong University of Technology, Zibo 255049, China;
2. Titanium Alloy Laboratory, Institute of Metal Research,
The Chinese Academay of Sciences, Shenyang 110016, China）
Abstract:The filling and solidification in centrifugal field, as well as the forming mechanism of off-center porosities were summarized, based on the mathematical model established for the centrifugal cast TiAl exhaust valves. The calculated results show that the centrifugal field results in the phenomenon that the flow in the valve cavity consists of forward flow and backward flow. The unsymmetrical initial temperature field causes continuous unsymmetrical variation in the following solidification, which makes the final solidified region depart from the cavity axis and then leads to the occurrence of off-center porosity. A series of optimized parameters, including the entrance velocity of 0.6-1.3m/s, the rotation speed higher than 300r/min, 80mm or longer entrance length and 400℃ or higher preheated temperature of the mold, are suggested for the manufacture of permanent mold centrifugal cast TiAl exhaust valves.
Key words: TiAl alloy; exhaust valve; permanent mold; mathematical model; off-center porosity
