Effect of Vanadium/Boron Ratio on the Microstructure of Al-V-B Master Alloy and Their Grain Refining of Alloy A356.2

Al-V-B is a promising grain refiner for anti-silicon poisoning in casting aluminum-silicon alloys, yet its optimal composition with excellent refining capabilities is still ongoing. Therefore, it is important to further investigate the impact of the vanadium/boron (V/B) ratio on the efficacy of Al-V-B refiner. In this work, the effect of varying V/B ratios on the microstructure of Al-V-B master alloys prepared by the fluorine salt method and their grain refinement of A356.2 alloy was investigated. The results indicated that with the variation of V/B ratio, the average particle size in Al-V-B master alloy ranges from 1 μm to 1.8 μm. Furthermore, when the V/B ratio exceeds 1:2, the primary phases present in the Al-V-B master alloy are VB₂ and coarse Al₃V. Conversely, when the V/B ratio is < 1:2, predominant phases in Al-V-B master alloy consist of small and uniformly distributed AlB₂ and VB₂. In addition, the grain refinement effect of Al-V-B master alloy on A356.2 alloy is significantly enhanced when the V/B ratio is < 1:2 and the grain size ranges from 215 μm to 234 μm. However, when the V/B ratio is > 1:2, the grain size of A356.2 alloy will increase.