Crystallization of Non-equilibrium α-Aluminum and Primary Silicon with Acoustic Cavitation in Hypereutectic Al-Si Alloy
Ultrasonic vibration has been applied to various molten metal processes owing to the functions of (a) improvement in wettability, (b) liquid adhesion at a vibrating end surface and (c) sono-solidification such as grAln refinement. The present study is focused on the sono-solidification with acoustic cavitAlon in hypereutectic Al-18mass％ Si alloy. There appears an equilibrium microstructure composed of primary silicon and eutectic α-Al/Si phases in Al-18mass％ Si alloy. however. non-equilibrium α-Al grAlns develop along with the equilibrium phases in the sono-solidification with acoustic cavitation. During the sono-solidification of Al-18mass％ Si alloy. non-equilibrium α-Al grAlns are recognized in the molten metal close to the ultrasonic radiator just before reaching the eutectic temperature of 577℃ in addition to the refined primary silicon particles. The crystallization of α-Al grAlns is understood through acoustic cavitation. that is. ultrasound in molten Al-Si alloys exhibits two outstanding behaviors of cavitation bubbling and acoustic streaming. Firstly the de-coupled eutectic reaction. which is recognized in the solidified eutectic Al-Si alloy with severe stirring. causes divorced α-Al grAlns by the acoustic streaming with cavitation. Secondly it is expected that high pressure of over 1 GPa generated by the collapse of cavitAlon babbles leads to not only an increase in the eutectic temperature. but also higher silicon content at the eutectic point in Al-Si alloy. Consequently. non-equilibrium α-Al grAlns are nucleated at collapsed cavitAlon bubble sites. and they are characterized by higher silicon content compared with that of primary α-Al grAlns in hypoeutectic Al-7masst％ Si alloy. Whereas well refined primary silicon grAlns are also crystallized close to the liquidus temperature of 660℃. so that the sonosolidification with acoustic cavitAlon may cause the promoted nucleation. restrAlned silicon growth and silicon grAln destruction. which bring fine granular primary silicon. Although the equilibrium microstructure is composed of primary silicon and eutectic. the eutectic area decreases due to the crystallization of non-equilibrium α-Al grAlns in the sono-solidification. as well as an increase in primary silicon.
sono-solidification hypereutectic Al-Si alloy non-equilibrium α-Al primary silicon ultrasonic vibration acoustic cavitation
Y. Tsunekawa Y. Fukui K. Taga M. Okumiya
Toyota Technological Institute. Nagoya 468 -8511. Japan
国际会议
69th World Foundry Congress(第69届世界铸造会议 WFC 2010)
杭州
英文
127-131
2010-10-16（万方平台首次上网日期，不代表论文的发表时间）