Thermal stability of Al2Si2Ce compound in Sr/Ce-modified cast and heat-treated A356 Al-alloys

A long-standing debate persists regarding the thermal stability of Ce-containing ternary compounds in Al-Si-based alloys; this dispute hinders the accurate design of high-performance Ce-modified Al-Si alloys. In this study, a combination of electron probe microanalysis (EPMA), X-ray diffraction (XRD), and transmission electron microscopy (TEM) was employed to elucidate the thermal stability of Al2Si2Ce compounds in cast and heat-treated alloys with different annealing mechanisms. First, the compositions of the Ce-containing compounds measured by EPMA were found to be quite similar to those of Al2Si2Ce, but with solubilities of < 1.5% Mg and < 0.5% Sr. Additionally, the XRD patterns further confirmed that Al2Si2Ce is the only stable compound found in the present alloy after casting and annealing at 535 °C. Subsequently, the TEM analysis revealed that the crystal structure of the Al2Si2Ce compound is hexagonal with a space group of P-3m1 (164), while its lattice parameters are a = b = 0.423 ± 0.002 nm and c = 0.689 ± 0.005 nm, which are in good agreement with the literature data. Finally, the crystal structure of the Al2Si2Ce compound and its atomic arrangement along three different zone axes were constructed by disregarding the occupation of the Mg and Sr atoms.