A grain refinement mechanism of cast commercial purity aluminium by vanadium

Abstract

Grain refinement of cast commercial purity aluminium by vanadium and the underlying mechanism have been investigated. Addition of 0.3 wt% and 0.4 wt% vanadium leads to columnar to equiaxed transition and the average grain sizes are refined to around 196 μm and 154 μm, respectively. Pro-peritectic equilibrium Al10V particles are identified near the grain centres. These Al10V particles have either octahedron or plate morphology with the bound planes belonging to {111} crystallographic planes. Three orientation relationships are also determined between the Al10V particles and aluminium grains. Crystallographic analysis based on the experimental orientation relationships indicates that the Al10V particles have relatively high nucleation potency for solid aluminium. Calculation of free growth undercooling based on the size distribution of the Al10V particles reveals that the relatively large size of Al10V particles facilitates the grain initiation of aluminium grains on these particles. Moreover, it is found that the level of vanadium added provides sufficient growth restriction effect in the aluminium melt as quantified by its growth restriction factor. All the three factors, i.e., sufficient potency of Al10V particles, relatively large size of the Al10V particles and adequate growth restriction effect by solute vanadium work in concert to achieve the grain refinement observed in Al-V alloys.