Refinement of primary silicon in hyper-eutectic Al-Si alloys by phosphor addition

Abstract

Effect of red phosphor addition to Al-Si, Sn-Si and Ag-Si alloys was studied with metallographic examination and line analyses on an X-ray microanalyses.Microstructures and line analysis charts of Al-25%Si alloys with 0.1%P and pure aluminum with 1.0%P are shown in photos 1 through 2 and those of Sn-6%Si and Ag-8%Si alloys with 2%P and 3%Al are shown in Photos 4 and 5. The results obtained are as follows:(1) When phosphor is added to molten Al or Al-Si alloys, a compound, commonly identified with AlP, is formed. When phosphor and aluminum are added together to molten Sn-Si or Ag-Si alloys, a compound, identified with AlP, is also formed.(2) With addition of P or P and Al together, grains of primary silicon in hyper eutectic Al-Si, Sn-Si and Ag-Si alloys are refined.(3) Most Al-P phases are included in refined primary silicon crystals. However, some AlP particles are also present in the matrix which is free from primary and eutectic silicon crystals.(4) When a metal mold is used, grain sizes of primary silicon and of AlP particles in silicon crystals as well as particle sizes of specimens, as a whole, became smaller than when a sand mold is used. The above experimental results seem to support the foreign nucleus theory which has been proposed to account for refinement effect of phosphor.