The purpose of this work is to model the dynamic microstructure evolution of aluminium alloys during hot metal forming processes such as extrusion. To this end, a phenomenological model based on the physical assumption that evolution of microstructure properties saturates after reaching the steady-state forming conditions is formulated. This model in combination with a thermo-elastic viscoplastic material model is implemented in the Finite Element (FE) software Abaqus. Simulation results for the microstructural development during extrusion as a function of process conditions demonstrate the sensitivity of microstructure development to these conditions. Comparison of the simulation results for the microstructure evolution with corresponding experimental results show good qualitative agreement.