High-temperature in-situ synthesis and formation mechanism of VB2 substrates in Al-V-B grain refiner

The uniform distribution of nucleant particles in the grain refiner is crucial for aluminum refining during inoculation. To address this issue, we propose a high-temperature in-situ synthesis method to produce the Al-1.61 V-0.62B grain refiner with uniform VB2 particle dispersion in the current research. The 2D microstructure of the master alloy shows the VB2 MaxFeret diameter ranges from 0.15 to 4.11 µm. Besides, 3D VB2 particles show inter-nested polygonal prismatic structures with facets on {0001} and {101¯0} surfaces and exhibit multiple growth morphologies. Theoretically, VB2 crystals nucleate on the V or B atomic clusters (or compounds), the pre-formed particle provides nucleation substrates for the post-formed particles, and the whole structure eventually evolves into a VB2 cluster. Thus, 3D VB2 clusters have a larger size range of 0.77–13.12 µm. The VB2 cluster formation mechanism explains the difference in 2D and 3D microstructures, as well as the VB2 particle agglomeration tendency. The 3D characterization of inoculated substrates is more accurate to evaluate whether the grain free-growth condition is satisfied or not. The outcomes of the present work may provide guidance for the development of V-B based master alloys with superior grain refining effects.