Equiaxed Grain Count in Aluminum Alloy Castings: Theoretical Background and Experimental Verification

In this work, a theoretical model is proposed for heterogeneous nucleation on substrates the size distributions of which can be described by the Weibull statistics. In particular, the proposed model suggests that the size distribution of the various nucleation sites is exponential in nature. It is found that the nuclei density can be given in terms of the maximum undercooling. Measurements of grain count were carried out on single-phase Al-1.3 Si and Al-5.0 Cu (wt pct) alloys inoculated using an Al-5Ti-1B (wt pct) master alloy. In the single-phase alloys, the area of equiaxed dendritic grains was estimated using EBSD analysis and by stereological means on polished and etched surface sections. In addition, maximum undercoolings were determined by thermal analysis. The experimental outcome indicates that the volumetric grain density can be properly described by an exponential expression. Finally, the magnitudes of the nucleation parameters were experimentally determined in this work.