Development of Non-Dendritic Microstructure of Aluminum Alloy in Semi-Solid State under Ultrasonic Vibration
The effect of processing parameters on the semi-solid microstructure has been investigated in the course of semi-solid slurry preparation of A356 Al alloy by ultrasonic vibration method. The A356 melt in temperature of 630660°C was poured into a special metal cup, and exposed to ultrasonic vibration at 20 kHz or isothermal holding for a certain time after vibration. The results show that the semi-solid slurry with primary α-Al crystals smaller than 90 μm and an average shape coefficient F S (SF was defined as SF4 A/L2P) above 0.5 could be prepared by ultrasonic vibration for a time less than 144 s. In the isothermal holding period after a short time of ultrasonic vibration, the average particle diameter increased with the increase of holding time, but F S decreased at first, and then increased a little. It was discovered that ultrasonic vibration is a good method to prepare semi-solid slurry with fine and relatively round primary crystals due to cavitation and acoustic streaming effects.
G. Hirt, A. Rassili, A. Bührig-Polaczek
S. S. Wu et al., "Development of Non-Dendritic Microstructure of Aluminum Alloy in Semi-Solid State under Ultrasonic Vibration", Solid State Phenomena, Vols. 141-143, pp. 451-456, 2008