Crystal Growth in Al_72.9Ge_27.1 Alloy Melt under Acoustic Levitation Conditions

The nonequilibrium solidification of liquid Al_72.9Ge_27.1 hypoeutectic alloy is accomplished by using single−axis acoustic levitation. A maximum undercooling of 112 K (0.16T_L) is obtained for the alloy melt at a cooling rate of 50 K/s. The primary (Al) phase displays a morphological transition from coarse dendrite under a normal conditions to equiaxed grain under acoustic levitation. In the (Al)+(Ge) eutectic, the (Ge) phase exhibits a conspicuous branched growth morphology. Both the primary (Al) dendrites and (Al)+(Ge) eutectics are well refined and the solute content of the primary (Al) phase is extended under acoustic levitation. The calculated and experimental results indicate that the solute trapping effect becomes more intensive with the enhancement of bulk undercooling.