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.