| In this study, the solidification behaviors and microstructure of Si-2O%Al alloy solidified at different undercoolings were investigated by means of electromagnetic levitation (EML) and high speed camera (HSC). Additionally, effects of addition RE and P on the solidification process and the as-solidified microstructure were also studied. The main results are shown as follows.For Si-20%Al alloy, when the undercooling is less than ΔT1(132 K), coarse flake-like primary silicon were recorded by HSC, and it exhibits pronounced edges and faces after solidification, suggesting that it grows as a lateral mode. When the undercooling is larger than ΔT2 (250 K), the recalescence interface reveals a straight planar, and fine grains with one or several stalactitic bulges on its surface of primary silicon can be seen from SEM observation, which shows the behaviors of continuous growth mode. As the undercooling ranges from ΔT1 to ΔT2, the recalescence interface is an irregular line. A mixtue of flake and blocky primary silicon can be observed in the microstructure. This indicates that the primary silicon grows as an intermediate mode between lateral one and continuous growth one.RE addition affects the solidification behavior and the as-solidified microstructure of Si-20%Al alloy. RE addition decreases two critical undercoolings, ΔT1 and ΔT2. The values of ΔT1 and ΔT2 are 100 K and 230 K for Si-20%Al-0.2%RE alloy, respectively. The values of ΔT1 and ΔT2 are 80 K and 210 K for Si-20%Al-0.5%RE alloy, respectively. The values of AT, and ΔT2 are decreased remarkably to 60 K and 199 K for Si-20%Al-1%RE alloy, respectively.The solidification behaviors of Si-20%Al alloy are greatly influenced through minor addition of P element. P addition not only decreases the nucleation undercooling, but also increases the effective nucleation sites of primary silicon. The nucleation undercooling of primary silicon within Si-2O%Al alloy is decreased to 15 K for Si-20%Al-1%P alloy. |
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