Grain refinement of pure Al using Al2.5Cu0.5Ti particles with an Ll2 structure

In this study, an L1(2)-modified Al2.5Cu0.5Ti intermetallic compound was chosen as a heterogeneous nucleation site to develop grain refiners for cast Al with a high volume fraction of heterogeneous nucleation site particles. Al2.5Cu0.5Ti intermetallic compound particles with an L1(2) structure were prepared by crushing the bulk material obtained by arc melting or directly by gas atomization. Al-10 vol% Al2.5Cu0.5Ti, Al-20 vol% Al2.5Cu0.5Ti, Al-30 vol% Al2.5Cu0.5Ti and Al-40 vol% Al2.5Cu0.5Ti refiners were fabricated by the spark plasma sintering method. The grain refining performance of the fabricated refiners for pure cast Al was investigated. It was found that fabricated Al-Al2.5Cu0.5Ti refiners were effective grain refiners for cast Al because Al2.5Cu0.5Ti particles with the L1(2) structure act as nuclei for Al grains in Al melts. Different refining performance characteristics appeared for refiners with different volume fraction of heterogeneous nucleation site particles, even though the total amount of particles in the melt was the same. Moreover, superior grain refining efficiency was obtained for the Al2.5Cu0.5Ti particles having a single phase than those with secondary phase. This is because the lattice matching between heterogeneous nucleation site particles and solidified Al is critical to obtain finer grain structures for Al casts.