An analytical model for the solution heat treatment in spherical alpha-solid particles is proposed. It is shown that there is a very good agreement between the prediction of this new model and available experimental measurements in literature. This analytical approach is similar to the Singh-Flemings model. The comparison of these models indicates that the prediction of solution heat treatment time in spherical alpha-solid particles is four times shorter than that of Singh-Flemings's model in dendrites under same conditions. If liquid segregation occurs during thixoforming, this may increase the amount of second phase and average composition in some regions of thixoformed products, therefore the solution time should be kept longer than the prediction of the theory for these pieces. For such a slightly liquid segregated structure, another analytical approach is proposed although it is not mathematically derived.