Primary phase transformation mechanism in a hypereutectic Al-Ce alloy during rapid solidification

Cooling rate plays an important role in determining the microstructure in as-cast aluminum alloys. To obtain a cooling rate gradient, a wedge Cu mould was selected. Here, we found a transition from hypereutectic to hypoeutectic microstructures in a hypereutectic Al-Ce alloy during rapid solidification. There was a distinct interface at a cooling rate of 1598 K/s. When the cooling rate was lower than 1598 K/s, the microstructures were composed of primary Al11Ce3 phases and Al/Al11Ce3 eutectic colonies. As the cooling rate was higher than 1598 K/s, the primary Al11Ce3 phases transformed into alpha-Al. Compared with the alpha-Al, the nucleation of Al11Ce3 phases was more favorable because of the lower nucleation energy. The growth rate of alpha-Al was higher than that of Al11Ce3 phases as the undercooling was larger than 182 K. Primary phase transformation mechanism in the hypereutectic Al-Ce alloy was controlled by nucleation and growth of alpha-Al and Al11Ce3 phases.