Correlation of composition, cooling rate and superheating temperature with solidification behaviors and microstructures of Al–Bi–Sn ribbons

Abstract

In this paper, Al85Bi6Sn9, Al75Bi9Sn16, Al60Bi14.4Sn25.6 and Al45Bi19.8Sn35.2 immiscible alloys ribbons were prepared using a single-roller melt-spinning technique. The influences of the composition, the rotating speed of copper roller and the melt superheating temperature were investigated in terms of the thickness, width, phase constitution and microstructures of Al–Bi–Sn ribbons. The results showed that the (Al), (Bi) and (Sn) solid solution phases existed in all the investigated Al–Bi–Sn ribbons. When the rotating speed was larger than 2000 revolutions per minute (rpm), the amorphous phase also was formed. The thickness of ribbons increased and the width decreased with the increase in the aluminum content or with the descent in the melt superheating temperature. The grain sizes of Sn–Bi-rich phase and Al-rich phase decreased gradually with the increases in the rotating speed, the aluminum content or the distance to the free surface. Although there was no obvious macrosegregation under the rapid solidification, the microsegregation still occurred under the rapid solidification. In addition, the grain size of Al75Bi9Sn16 ribbons had a minimum value after the melt superheating treatment at 910 °C. The impact of melt thermal treatment on the microstructure was analyzed from the views of thermodynamics and kinetics. The changes in the grain size and morphology were attributable to the differences in migration rate, solidification rate and the time of liquid-liquid phase separation (L-LPS). The results are conducive for understanding the effects of composition and melt treatment on the microstructures of immiscible alloys.