A comparison of acoustic levitation with microgravity processing for containerless solidification of ternary Al–Cu–Sn alloy

The containerless rapid solidification of liquid ternary Al–5 %Cu–65 %Sn immiscible alloy was accomplished at both ultrasonic levitation and free fall conditions. A maximum undercooling of 185 K (0.22 T_L) was obtained for the ultrasonically levitated alloy melt at a cooling rate of about 122 K s⁻¹. Meanwhile, the cooling rate of alloy droplets in drop tube varied from 10² to 10⁴ K s⁻¹. The macrosegregation was effectively suppressed through the complex melt flow under ultrasonic levitation condition. In contrast, macrosegregation became conspicuous and core–shell structures with different layers were formed during free fall. The microstructure formation mechanisms during rapid solidification at containerless states were investigated in comparison with the conventional static solidification process. It was found that the liquid phase separation and structural growth kinetics may be modulated by controlling both alloy undercooling and cooling rate.