The Structural Evolution of Al-6Y-2P Master Alloy and its Influence on the Refinement of Mg2Si Phase in Mg2Si/Al Composites

In this article, a novel Al–6Y–2P master alloy with YP particles was successfully synthesized. By means of the fracture surface observation, it was found that YP particles with an average size of 21.5 μm exhibit the cubic morphologies. With the addition of Al–6Y–2P master alloy, primary Mg2Si particles in Al–Mg2Si composites can be significantly refined to 21.2 μm and 20.3 μm after holding for 30 min and 120 min respectively. Meanwhile, the morphologies of eutectic Mg2Si alter from a flake-like to fine fibrous shape. The reason for the excellent refining performance of this master alloy was discussed based on the chemical kinetics theory. During the solidification process, P atoms distribute homogeneously in the Al melt and precipitate in the form of AlP, providing heterogeneous nucleation sites for primary Mg2Si.