Impact of TiB₂ Particle Size Distribution on Grain Refining Effectiveness

Grain refiners of the Al–Ti–B system, including TiB₂ particles, are added to molten aluminum to produce the fine grains. The effect of grain refinement significantly fluctuates among grain refiner manufacturers and the lots despite the same composition. Furthermore, although various features for the grain refiners exist, it is unclear which feature is the most effective for grain refining. The mechanism of grain refinement has been proposed that the TiB₂ particles act as heterogeneous nuclei. The free growth model has become the standard model for the action of grain refining. This model assumes that the TiB₂ particle size distribution influences the inoculation efficiency. However, there are few examples that verified the inoculation efficiency using a grain refiner with different TiB₂ particle size distributions. In this study, the grain refinement effectiveness of several grain refiners using different manufacturers and different compositions was investigated. The TiB₂ particle size distribution in the grain refiner was measured by image analysis and applied to the grain size prediction model which was developed based on the free growth model. The experimental and calculated results were compared and discussed in order to clarify whether the new model can predict the grain size inoculated with each refiner.