Magnesium with its density of 1,8 g/cm is the lightest useable commercial metal. Consequently, it is ideal for light weight constructions. Further advantages are good processability, machinability and recyclability. Nowadays due to the increasing pressure to construct more cost-efficient and weight-reducing at the same time, the magnesium as a construction material gets rediscovered. High-pressure die-casting is the most common production process for magnesium components. It is used to obtain components with complex geometries at high production rates. The main problem of components made by high-pressure die-casting is connected with inherent flaws (pores, oxide skins, etc.), which can be hardly avoided. For improved design of these components on fatigue strength, it is necessary to derive models, for both material characteristics as well as inherent flaws of the production process. There is an existing porosity model [34] for the estimation of porosity within high-pressure die-casting components. One part of this assignment was, with the help of this approach, to prove the application and find the parameters of the model for the die casting alloy AZ91hp. With the analysis of the porosity of the plate, one was able to find a relation with the results of the casting process simulation. As a result, it was possible to predict the porosity of the plate based on the casting process simulation. The characterization of the fatigue strength for AZ91hp led to a huge distribution among the data within the stress level for the dynamic tension/compression tests. This distribution is caused by the different defect sizes in the specimen cross section. Therefore, a crack initiating defect area in each fracture surface has to bee found to get further information about the test results. With these results a material model was developed in order to derive a defect size dependent S/N-curves for each element in the component from a pore free S/N-curve.