INCORPORATION OF ALUMINA PARTICLES WITH DIFFERENT SHAPES AND SIZES INTO MOLTEN ALUMINUM-ALLOY BY MELT STIRRING WITH ULTRASONIC VIBRATION

This paper presents the influence of particle shapes and sizes on the incorporation of Al2O3 particles into molten Al-5 mass%Mg alloy by mel t stirring with ultrasonic vibration. A new theoretical model of parti cle transfer into molten metal dealing with different shapes is propos ed to estimate the difficulty in incorporation of spherical and massiv e particles. In the model, the particles are assumed to be spheroids w ith different major and minor axes. The difficulty depends on the maxi mum acceleration which originates from the interfacial tension: the in corporation of Al2O3 particles into molten Al-Mg alloy becomes more di fficult with the negative maximum acceleration increased. Four kinds o f preheated Al2O3 particles were added to a molten Al-5 mass%Mg ahoy s urface and stirred with ultrasonic vibration at 1023 K in a nitrogen a tmosphere. The volume fraction of incorporated particles is related to the calculated maximum acceleration; that is, it is experimentally fo und to decrease as the negative maximum acceleration increased. accord ing to the proposed model, the ultrasonic vibration makes the apparent contact angle of the Al2O3 particle and the molten Al-Mg ahoy improve from 1.78 to 0.87 rad. Gas defects, which are known to be a serious p roblem in metal matrix composites (MMC) produced by melt stirring, dis appear in MMC samples formed with ultrasonic vibration. Moreover, the rotating torque for melt stirring decreases by applying ultrasonic vib ration, because of the decomposition of agglomerate particles. Hence, the application of ultrasonic vibration to melt stirring is a novel ca ndidate method of MMC production.