Effect of phosphorus additions on the spacing between primary silicon particles in a Bridgman solidified hypereutectic Al-Si alloy

The effect of 100 ppm addition of phosphorus on primary silicon particle number density per unit area NA and corresponding interparticle spacing λ is reported for a Bridgman solidified Al-20 wt%Si base alloy. The phosphorus (added as Al-Fe-P base or Al-Cu-P alloys) results in a factor of 3 increase in NA and a factor of 2 reduction in λ for the range of conditions studied. In its absence the results conform to λ\(\dot T^1/3 \) = 256 ± 24 μm (K/s)1/3 where \(.dot T\) is cooling rate during solidification in good agreement with earlier data. When published data on the effect of 0.02 to 0.2 wt%P are included the combined results are well represented by λ\(\dot T^1/3 \) = 250 − 215 (wt%P)0.17 (λ in μm, \(.dot T\) in K/s).