Refining and nucleating behaviors of AlP on primary phase in Al–Ge and Al–Ge–Si alloys

The present study addresses refining behavior of AlP on primary phases in Al–Ge and Al–Ge–Si alloys. In binary hypereutectic Al–70Ge alloy, the addition of Al–P master alloy leads to a refinement performance for primary Ge. It is found that AlP can act as the nucleation sites for primary Ge particles, and between them the lattice mismatch is 3.85%. Besides, the introduction of AlP in Al–Ge alloy results in an increased undercooling for the precipitation of primary Ge. While for Al–60Ge–5Si alloy, Si and Ge form continuous solid solution, with Si distributing in the center of the primary particles and Ge the outer layer. The primary solid solutions can also be significantly refined by AlP. Moreover, due to the nucleation behavior of AlP particles, primary Si crystals doped with a certain amount of Ge are refined to about 30 μm from more than 140 μm in Al–20Ge–18Si alloy.