Effect of treatment variables on size refinement by phosphide inoculants of primary silicon in hypereutectic Al–Si alloys

Abstract

The effects of phosphorus containing inoculant identity/process history, addition level, addition temperature, and contact time on number density N _A of primary silicon particles in small volumes of cast Al–20 wt-%Si are reported. Inoculation replaces the coarse, branched primary silicon otherwise obtained in the upper part of these castings with a uniform distribution of small polyhedral primary silicon particles. The inoculants tested increased in effectiveness in the sequence: die pressed and heat treated Al–Fe–P; die pressed Al–Fe–P; extruded Al–Cu–P; and Al–Fe–P prepared by a proprietary route. This last inoculant gave a maximum N _A at 200 ppm addition level in this volume of melt for a contact time of 10 min at 800°C, and at 10 min contact time for an addition level of 100 ppm at this temperature. An addition temperature of 850°C produced a small reduction in N _A, compared with 750 or 800°C. The significance of these findings is discussed in the context of previously published work and possible mechanisms leading to less effective inoculation at high addition levels and extended contact times.