The nature of the cast microstructure and its heterogeneity affect the fluidity of the alloys, the formation of shrinkage voids, the kinetics of linear shrinkage, and the occurrence of hot cracks. The paper investigates the inhomogeneity of the dendritic and eutectic structural components formed in the multicomponent aluminum alloy AK12 at different cooling rates (from 0.02 to 11 K/s). The kinetics of change and morphology of the local dendritic and/or dendritic-eutectic structure are described in this work using computer analysis of the nonequilibrium crystallization of the alloy in combination with a statistical study of a significant array of experimental data on the microstructure of the AK12 alloy. Using the methods of mathematical statistics, the log-normal nature of the mesoscale inhomogeneity was established at the stage of separation of the primary solid solution and during the subsequent eutectic transformation.