Effects of rapid solidification and Ce on the microstructure of Al–40Si

Abstract

ABSTRACT This work explores the use of Ce and rapid solidification to attain primary Si modification in a hypereutectic Al-40wt-%Si alloy. Al–40Si and Al–40Si–1.5Ce powders were produced by Impulse Atomization. The resulting powders having increasing liquid cooling rate from ∼103 to ∼105 K/s were studied to determine the effect of Ce on the microstructure. The microstructures of both alloys contained an Al-rich halo (α-Al) which is not part of Gulliver-Scheil solidification paths. The presence of this structure suggests solidification of both alloys deviated from local equilibrium. In both alloys, increasing cooling rate was associated with the formation of less elongated primary Si presenting a more rounded surface. Additionally, alloying with Ce improved the distribution of primary Si in the microstructures of the smallest powders. Quantitatively, the microstructures of both alloys were found to increase in primary Si and halo (α-Al) content as cooling rate increases. The use of Ce also led to a measurable decrease in eutectic content in Al–40Si–1.5Ce with respect to the unmodified alloy. Similarly, primary Si and halo (α-Al) vol.-% also appear to increase as a result of Ce addition.