Grain refinement of alloys by inoculation of melts

Recent progress in understanding the inoculation of aluminium melts is reviewed. Transmission electron microscopy of inoculant particles in a metallic glass reveals details of the mechanism of nucleation of aluminium grains. While such studies define some of the conditions under which inoculation is effective or not, they do not permit a prediction of grain size. Unusually for a nucleation–related phenomenon, quantitative prediction is possible. For potent inoculation such as is practised in aluminium alloys, grain initiation is limited by inoculant particle size, occurring first on the largest particles. Simple thermal models can then describe the dependence of grain refinement on alloy content and processing conditions, and enable consideration of inoculant design.