Effects of cerium on as-cast microstructure of AZ91 magnesium alloy under different solidification rates

In order to research the different effects of Ce on as-cast microstructure of AZ91 magnesium alloy under different solidifi- cation 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-Mg17A112 phase, form A14Ce phase and decrease solid solution of A1 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 A1 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 AI in α-Mg matrix. However, the dynamic condition of concentration of Ce, A1 would be changed when solidifica- tion rate varied, resulting in different influence extents of Ce on as-cast microstructure under different solidification rates.