In order to research the different effects of Ce on as-cast microstructure of AZ91 magnesium alloy under different solidification rates, the die-cast samples with different diameters and different Ce contents were prepared, and some characteristics of as-cast microstructure were analyzed. The results showed that Ce could refine grain size, decrease the fraction of eutectic β-Mg_(17)Al_(12) phase, form Al_4Ce phase and decrease solid solution of Al in the α-Mg matrix, but the above behaviors of Ce would be weakened under higher solidification rate. The essential reason for Ce to affect as-cast microstructure was that the Ce and Al concentrated in the liquid phase in front of solid/liquid interface during solidification because Ce itself is difficult to solid solute in α-Mg matrix and inhibits solid solution of Al in α-Mg matrix. However, the dynamic condition of concentration of Ce, Al would be changed when solidification rate varied, resulting in different influence extents of Ce on as-cast microstructure under different solidification rates.
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