Solidification pathways in the Al‑rich part of the Gd–Al–Si system

The effect of gadolinium addition to the Al–Si system (in the aluminum rich corner) has been experimentally studied, as the invariant reactions involved during cooling from the molten state and the liquidus projections. The thermal behavior has been investigated by means of Differential Thermal Analysis (DTA), and the constitution of the alloys has been determined through scanning electron microscopy (SEM), electron microprobe analysis (EDS) and X-ray powder diffraction. Knowledge of the phase relationships in the R–Al–Si ternary systems (R: rare earths element) is essential to deeply understand the technological properties of the Al–Si-based alloys, that are useful in different industrial fields. In the system investigated have been experimentally determined two primary crystallization fields: GdSi2 dissolving aluminum up to 6 at% and GdAlSi (Ƭ2 compound) at an aluminum concentration range from 28.5 to 36 at%. The ternary equilibria determined are: the ternary eutectic L ⇄ (Al) + (Si) + GdAl2Si2 and the U invariant equilibrium L + T2 ⇄ GdAl2Si2 + (Al). The results obtained can be useful for predictive purposes when compared with other well-known R–Al–Si systems.