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 Delta T-min (Delta T-min is the difference between the minimal overheating temperature T-min and the liquidus temperature T-L) for good refinement is about 260 degrees 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 mu m. The X-ray diffraction data of the Al-50Si melt demonstrate that structural change occurs when the melting temperature varies from 1100 degrees C to 1300 degrees C. Additionally, the relationship between the refinement mechanism and the melt structure is discussed. (C) 2008 Elsevier Inc. All rights reserved.