Grain refinement of aluminum alloys

A better understanding of the mechanisms of grain refinement can contribute to the development of better refiners and to improved industrial practice. Recent studies of refinement mechanisms are reviewed, focusing on grain initiation on nucleant particles and on the effects of solute content in the melt. Microscopical studies of nucleant particles have been particularly useful in analyzing the adverse (poisoning) effects of certain solutes. Using a particular model for grain initiation, quantitative predictions can be made for the variation of as-cast grain size with alloy composition, refiner addition level, and cooling rate. Comparison is made with results from small-scale tests and full-scale DC casting. Possibilities for improvement of refiners are assessed, and some areas requiring further research are highlighted.