The investigations give an insight into micro-galvanic corrosion processes at the model system Mg-Al. Required boundary conditions are determined by the surface morphology of the binary Mg-9Al alloy, and by electrochemical kinetics of the different metallic phases. In order to model the problem micrographs of casted alloys were transformed into a model geometry. The computations show how e. g., the conductivity of the electrolyte determines the corrosion process. The arising possibilities of the modeling support the development of alloys with respect to their corrosion properties by simulations. Thus, the work provides impulses for the innovative topic of simulation based corrosion protection.