Optimal holding temperatures and phosphorus additions for primary silicon refinement in Al-high Si alloys

The refinement of primary silicon particles in hypereutectic aluminium-silicon alloys with exceptionally high Si contents (Al-high Si alloys) has been studied using optical microscopy, scanning electron microscopy and electron probe microanalysis. A new Si-20P master alloy has been developed which was used to study the optimal melt treating technology for achieving a satisfactory refinement of primary silicon. The experimental results show that the optimal superheating temperature and the amount of phosphorus addition increase abruptly when silicon content reaches about 50 wt-%. A few of experiential formulae are presented for the optimal superheating temperature and the amount of phosphorus addition. The refinement mechanism of the primary silicon is also discussed.