Grain Refinement of Cast Aluminum by Heterogeneous Nucleation Site Particles with High Lattice Matching

A number of studies have been carried out to identify the mechanism of grain refinement in cast aluminum alloys by addition of grain refiners containing potent heterogeneous nucleation site particles. Although some mechanisms and theories have been proposed, in this review, the role of heterogeneous nucleation site particles on grain refining performance will be focused. The content of this article is as follows. First, the morphology of Al₃Ti particles in the Al-Ti refiners is presented, since the grain refining performance of the Al-Ti refiners is affected by the morphology of the Al₃Ti particles. Evaluation methods of lattice matching between heterogeneous nucleation site and crystallized phase are, then, discussed. Since we conclude that M value is potentially applicable to predict the effective heterogeneous nucleation site, M value at elevated temperatures is described. Next, fragmentation behavior of Al₃Ti particles caused by deformation of the refiners is presented, because the number density of the Al₃Ti heterogeneous nucleation site particles is increased by the fragmentation of Al₃Ti particles. At the same time, the morphology of the Al₃Ti particles, which affects the grain refining performance, can be changed. The concept of grain refiners with high-symmetry L1₂ modified (Al₁−_xMe_x)₃Ti intermetallic compound particles, fabrication method and some results on grain refining performance are also given. Finally, application of heterogeneous nucleation for other fields are described.