Effect of Glass Tube Suction Casting on Solidification Process and Si Refinement of Hypereutectic Al–Si Alloy

This study unpicks the influence of the glass tube suction casting (GTSC) with different inner diameters (8, 10, 12 and 14 mm) on the solidification process of the hypereutectic Al–Si alloy (A390) and dissects the underlying mechanisms of the Al–Si divorced eutectic and refinement degree of the primary silicon particles (PSPs). The results show that a smaller inner diameter of the glass tube is more favorable for achieving Al–Si divorced eutectic in GTSC A390 alloy. Conversely, a larger inner diameter is more conducive to the formation of the lamellar eutectic Si. The GTSC A390 alloy with an inner diameter of 10 mm achieves the smallest average equivalent diameter (approximately 7.4 μm) of the PSPs. Being the prior diffusion channels for solute atoms, the grain boundaries and twin growth grooves of PSPs attract solute atoms (Cu, Mg, etc.) to enrich. The enriched solute atoms occupy the diffusion destinations of some Si atoms, which limits the overall growth of PSPs. These findings provide new insights into developing a simple and effective manufacturing process to refine the primary and eutectic Si phases in hypereutectic Al–Si alloys.