Experimental study of the solid-liquid equilibria in the Gd-Al-Si ternary system

The integration of rare earth elements into aluminum-silicon (Al-Si) alloys has become a focal point for the development of light alloys materials with enhanced mechanical and thermal properties. Previous studies [1] highlighted how gadolinium significantly alters the phase diagrams of the Al-Si system, favoring the formation of stabilizing intermetallic phases. This study emphasizes the transformative potential of gadolinium in Al-Si alloy systems, aiming to provide a deeper understanding of their scope for application in advanced industrial uses and extreme operational environments, allowing to design new alloys dedicated to specific purposes. This experimental work focuses on the influence of gadolinium, a lanthanide, on the properties of Al-Si alloys, highlighting the liquid solid equilibria under melting. The ternary alloys were directly synthesized and characterized by means of Differential Thermal Analysis (DTA), X-ray Powder Diffraction (XRPD), and Scanning Electron Microscopy (SEM). The system has been studied in the aluminum rich corner as the industrially relevant R-Al-Si alloys have usually compositions lying in the aluminum rich part of the phase diagram. Figure 1 shows the liquid projection of the Gd-Al-Si system. Three ternary compounds have been recognized in the system: GdAl2Si2(τ1) hP5-CaAl2O2, GdAlSi (τ2) tI12-ThSi2 and Gd4AlSi 3(τ3) oC8-CrB. As the solidification equilibria, the following have been identified: • three regions of primary crystallization: Si, τ2 and βGdSi. • one ternary eutectic transformation: L ⇄(Al) + (Si) + τ1 at about 567°C. • one invariant equilibrium: L+ GdAlSi ⇄GdAl(3-x)Six + L’ at about 580°C.