The influence of Gd content on the solidification and microstructure of AlSi7Mg0.3 casting alloy

The effects of Gd content on the solidification path and microstructure of an AlSi7Mg0.3 alloy have been studied. Two different Gd levels, 0.1 and 0.5 mass%, respectively, have been investigated while the material has been solidified at low (0.2 degrees C s-1) and high (1.3 degrees C s-1) cooling rates. Computer-aided thermal analysis and metallographic techniques have been used to study the solidification and microstructural evolution of the alloy at different Gd contents and cooling rates. The results show how Gd has no effect on the grain refinement at both cooling rates. The eutectic structure is unaffected at Gd level of 0.1 mass%. A concentration of 0.5 mass% Gd promotes the precipitation of the gadolinium phosphide (GdP) phase instead of aluminium phosphide (AlP) compounds, thus suppressing the eutectic plateau during the solidification and serving as nucleant for the GdAl2Si2 phase. The eutectic Si crystals solidified at low cooling rate are refined at 0.5 mass% Gd content, while the morphology of Si crystals is only partially modified at high cooling rate.