Modelling of inoculation of metallic melts: Application to grain refinement of aluminium by Al-Ti-B

A numerical model is presented for the prediction of grain size in inoculated castings and is tested against measured grain sizes obtained in standard grain-refiner tests on aluminium alloys. It is shown that for potent nucleants, such as commercial grain refiners for aluminium, the nucleation stage itself is not the controlling factor. The number of grains is determined by a free-growth condition in which a grain grows from a refiner particle at an undercooling inversely proportional to the particle diameter. With measured particle size distributions as input, the model makes quantitatively correct predictions for grain size and its variation with refiner addition level, cooling rate and melt composition. The model can assist in optimizing the use of existing refiners and in developing improved refiners. (C) 2000 Published by Elsevier Science Ltd on behalf of Acta Metallurgica Inc.