Effect of RE Addition on the Solidified Process and Microstructure of Al-7Si-0.3Mg Alloys

Abstract

The solidification process and microstructure of Al-7Si-0.3Mg alloy with different rare earth (RE) additions have been studied by using thermal analysis, optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The results showed that the addition of RE enhanced the liquidus temperature and decreased the growth temperature of eutectic Si, which lead to obvious increase in solidification interval of the studied alloy. In addition, the grain size of primary α-Al had no obvious change, and the mean area of eutectic Si particles decreased with increasing RE content to 1.6 wt.%. The RE-rich compounds with different compositions were obtained with increasing RE concentration in Al-7Si-0.3Mg alloys. The method of phase diagram calculation helps to clarify the formation and growth mechamism of different RE-rich phases during solidification.

Study on mechanism of refining and modifying in Al–Si–Mg casting alloys with adding rare earth cerium

“…Combined with the point scanning results of point C (Si: Mg: Fe ≈ 6:3:1) shown in table3, This phase was determined to be the π-Al 8 Si 6 Mg 3 Fe phase. At the same time, the bright bulk phase is mainly enriched by Al, Si, and Ce elements, and from the point scan results of point D, the atomic percentage content ratio of Ce and Si is about 1:2, confirming that this phase is AlCeSi 2 phase[21,26].…”

“…a s is the lattice parameter of the α-Al phase; a n is AlCeSi 2 The lattice parameters of the phase; after calculation, the lattice mismatch between the α-Al phase and the AlCeSi 2 phase is 2.96%, less than 5%, which can theoretically be used as the heterogeneous nucleation core of α-Al to refine the effect of the grain. In the solidification process of Al-Si-Mg experimental alloy, a small amount of AlCeSi 2 phase is generated at 598 °C [26], and the initial nucleation temperature of the binary eutectic reaction is 564.87 °C from table 4, indicating that the AlCeSi 2 phase is preferred to the eutectic Si nucleation, eutectic Si can rely on the growth of AlCeSi 2 phase, the formation of AlCeSi 2 phase can consume part of Si elements, AlCeSi 2 inhibits the growth of eutectic Si, thereby refining eutectic Si. At the same time, the solubility of Ce in Al and Si is extremely small, and Ce will be enriched to the front of the solid-liquid interface to hinder the growth of surrounding α-Al grains (figure 9(f)), thus playing a role in refining the structure.…”