Refinement performance and mechanism of an Al-50Si alloy

The microstructure and melt structure of primary silicon particles in an Al-50%Si (wt.%) alloy have been investigated by optical microscopy, scanning electron microscopy, electron probe micro-analysis and a high temperature X-ray diffractometer. The results show that the Al-50Si alloy can be effectively refined by a newly developed Si-20P master alloy, and the melting temperature is crucial to the refinement process. The minimal overheating degree ΔTmin (ΔTmin is the difference between the minimal overheating temperature Tmin and the liquidus temperature TL) for good refinement is about 260 °C. Primary silicon particles can be refined after adding 0.2 wt.% phosphorus amount at sufficient temperature, and their average size transforms from 2–4 mm to about 30 μm. The X-ray diffraction data of the Al-50Si melt demonstrate that structural change occurs when the melting temperature varies from 1100 °C to 1300 °C. Additionally, the relationship between the refinement mechanism and the melt structure is discussed.