The performance of castings is primarily dependent on the solidification microstructures and defects.Gas porosity is one of the major casting defects existing in the castings of lightweight materials,such as aluminium and magnesium alloys.In this talk, a two dimensional (2D) cellular automaton (CA)-finite difference method (FDM) model and a CA-lattice Boltzmann method (LBM) model are presented for the simulation of dendrite growth and microporosity formation during alloy solidification.The models involve a three-phase system of liquid, gas, and solid.The effect of liquid-solid phase transformation on the nucleation and growth of gas pores are taken into account.