This master thesis focuses on the fatigue behaviour of the magnesium die casting alloy AZ91hp. The reduction of carbon dioxide and a reducing availability of fossil energy are the reasons, why many industrial sectors focus on lightweight construction. One possibility is to benefit from the low density of magnesium alloys. Magnesium is the lightest commercial metal. High-pressure die casting (HPDC) is a cost-effective technique to produce magnesium components but the components exhibit flaws, like pores, shrinkage porosity or other oxides. Oberwinkler [1] proposed a model to estimate the pore distribution of HPDC AlSi9Cu3. Reichhart [2] adapted this model to a plate with constant thickness made of AZ91hp. One of the aims of this work is to prove the applicability and transferability of this model to a reference part with varying wall thickness. A correlation between the casting process simulation and the porosity of the reference part was found. Now it is possible to predict the pore size distribution based on the results of the casting process simulation for the magnesium alloy AZ91hp. The improvement of fatigue strength moves more and more in the centre of development. Mechanical components often collapse under multi-axial loading, which influences the lifetime considerably. AZ91hp is characterized under uni- and multi-axial loading. The test results are compared with results of lifetime calculations using different strength hypotheses. The Safety Factor Intensity Hypothesis (SFIH) and the elliptic criterion after Gough show the best analogy. The prediction of porosity and the determined material parameters enable a drastically improved computation of the fatigue safety factor. [1]Oberwinkler C.: "Virtuelle betriebsfeste Auslegung von Aluminium-Druckgussbauteilen", Dissertation, Leoben, 2009 [2]Reichhart M.: "Quantifizierung von fertigungsbedingten Defekten und deren Einfluss auf die Schwingfestigkeit der Magnesiumdruckgusslegierung AZ91hp", Diplomarbeit, Leoben, 2008