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Phosphorus-Copper as a Nucleant

Phosphorus-Copper is used as a nucleant in greater than 11% Silicon-Aluminum. When added to Silicon-Aluminum, Phosphorus-Copper forms AlP, which causes silicon to solidify as small, blocky particles instead of long, brittle fingers. This results in improved toughness, wear-resistance, castability and machinability.

Recommended Addition Procedure:

  1. Calculate the addition of 0.02% to 0.04% precisely.
  2. Adjust the metal temperature to 1335° to 1450°F (724° to 788°C).
  3. Skim drosses.
  4. Broadcast 8% Phosphorus-Copper shot over as wide an area as possible.
  5. Wait five (5) minutes.
  6. Gently, but thoroughly and mechanically, hand-mix the bath. Do not depend on gas bubble stirring, which tends to remove the phosphorus.


  • The reaction of Cu3P to AlP is very hot and very fast.
  • AlP tends to float. If it is in contact with the air, it vigorously forms aluminum oxide and phosphorous pentoxide, which burns.
  • The more phosphorus added, and the more concentrated the addition agent, the hotter the reaction. The AlP particles will be larger and will rise and burn faster than you will be able to cast the treated alloy.
  • Add 8% Phosphorus-Copper instead of 15%
  • Add fine shot instead of coarse shot.
  • Add Phosphorus-Copper later in the process rather than earlier.
  • Always keep Phosphorus-Copper DRY.
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