A microsegregation model for the solidification of binary alloys is presented. It accounts for diffusion in all phases, as well as nucleation undercooling and growth kinetics of the solidifying microstructures. It successively considers the occurrence of several phase transformations, including one or several peritectic reactions and one eutectic reaction. Volume-averaged mass conservation equations are coupled with a heat balance assuming a uniform temperature. The model is applied to simulate the solidification of Al–Ni atomized droplets. Coupled with an atomization model, it predicts recalescences, volume fractions of phases as well as average compositions during solidification. It eventually predicts the occurrence of a recalescence during the growth of each microstructure, and the progress of peritectic transformations consuming previously formed solid phases. The influence of several process parameters is evaluated. A comparison with experimental measurements is given, showing variation of phase fractions as a function of particle size for Al–Ni atomized droplets.