Application of ultrasonic vibration to in situ MMC process by electromagnetic melt stirring

In situ process based on melt stirring, in which reinforcements are newly formed during the process, is expected to be a major production method of MMC components, because thermodynamically stable reinforcements are formed from inexpensive raw materials such as SiO2. However, it is confronted with the difficulty of long processing time at high temperatures to transfer SiO2 particles into molten aluminum alloy and to form stable oxides. Since such a difficulty arises from poor wettability, with the aim of forcible improvement in poor wettability by applying ultrasonic vibration, the preparation of sound composite slurry containing stable oxides was carried out by electromagnetic melt stirring. The forcible improvement in wettability is confirmed by a decrease in contact angle, when a SiO2 sphere was immersed into molten AI-Mg alloy with ultrasonic vibration. Added SiO2 particles as an oxygen source rapidly transfer and exothermally react with molten A-Mg alloy, which contributes to an increase in molten matrix temperature. By electromagnetic stirring with ultrasonic vibration, the amount of SiO2 particles transferred into molten aluminum alloy is promoted compared to that without ultrasonic vibration, because of the improved wettability. The transferred SiO2 particles are quickly turned into stable oxides, MgAl2O4 and Al2O3. Hence, the application of ultrasonic vibration makes not only the transfer and reaction rate of SiO2 particles remarkably fast, but also porosities caused by atmospheric gas entrapment eliminate. Then, the original matrix of AI-Mg alloy changes into AI-Si due to the reduction of SiO2 particles. (C) 2001 Elsevier Science Ltd. All rights reserved.