IN-SITU FORMATION OF STABLE OXIDES IN MOLTEN ALUMINUM-ALLOY BY ULTRASONIC STIRRING

This study is aimed at examining the influence of ultrasonic vibration on the in-situ formation of stable oxides, Al2O3 and MgAl2O4, from Si O2 particles added as an oxygen source in melt stinting. The preheated SiO2 particles were added on a molten Al or Al-Mg alloy surface and s tirred at 1073 K in an Ar atmosphere. The ultrasonic vibration was the n transmitted to molten metal through a ceramic plate. The SiO2 partic les are not transferred into the molten Al by melt stirring without ul trasonic vibration. With ultrasonic vibration, the SiO2 particles, whi ch have been transferred into the molten Al due to the improved wettab ility, change to stable Al2O3. The transferred SiO2 particles into the molten Al-Mg alloy change to MgAl2O4 and Al2O3. The application of ul trasonic vibration to melt stirring makes not only the wettability imp rove, but also the cracks in the particles grow, which arise from the volumetric shrinkage accompanied with the change from SiO2 to MgAl2O4 and Al2O3. The stable oxides are rapidly formed due to the fast diffus ion of Al and Mg through the cracks. The exothermic reactions of MgAl2 O4 and Al2O3 formation lead to a temperature rise in the molten Al-Mg alloy, in which the temperature rise of 99 K is approved by applying t he ultrasonic vibration. Consequently, the in-situ reactions are promo ted further. Gas defects disappear in the solidified Al alloy containi ng the stable oxides stirred with ultrasonic vibration, in which the p article distribution is also improved.