Grain refinement of aluminum alloys: Part I. The nucleant and salute paradigms - A review of the literature

Despite the extensive literature on grain refinement, there is not a consensus on the mechanism of grain refinement in aluminum alloys. Recently, there has been a shift in understanding of the grain refinement paradigm from purely being concerned with the nucleation event, called here the "nucleant paradigm," to also being concerned with the effect of solute elements, or, the "solute paradigm," on the final grain structure. This article is divided into two parts. In Part I, the literature underpinning both paradigms is explained, and the validity of the paradigm shift toward the solute paradigm as a more complete understanding of grain refinement is presented. Part II experimentally confirms the validity of the solute paradigm and details a mechanism which explains the need for both effective nucleants and a solute of a good segregating power in order to obtain grain refinement.