Aluminum as a material for components of the automotive sector is gaining on industrial importance, especially through modern casting processes complex designs can be economically realized. The cast aluminium surfaces are not mechanically finished in some cases, which is why a judgment of surface effects regarding fatigue strength is technologically utmost relevant. This master thesis focusses on the investigation of surface layer effects and their impact on fatigue strength. In order to be able to examine the surface layer structure caused by the casting molds, flat samples with surfaces in as-casted condition are taken out of two characteristical cylinder crankcase (ZKG) series to study their effect on fatigue strength. In addition, samples of ZKG have to be studied which are post-treated by hot isostatic pressing (HIP), which omit cyclic failures due to volumetric continuum defects. Subsequent experimental investigations with regard to surface topography as well as an analysis of the fractured surfaces should feature a more definite fatigue strength evaluation of the casted surface layer. At first, the cast-aluminum surface of each sample is scanned non-destructively with a digital light microscope and surface characteristics as well as other topographical characteristics are evaluated. Cyclic tests are carried out under tumescent bending stress in order to preferably initiate the crack initiation in the edge layer of the cast aluminum surface. The investigations reveal that the existing geometrical notch, which is based on the mold parting line, possesses a dominant influence on the fatigue strength. The influence of the surface roughness is also investigated thoroughly, but it is less pronounced compared to the influence of the mold parting line in terms of the cast notch. The notch stress concentration factor is determined by numerical finite element analysis and the local notch stress course is evaluated for both series. The use of a batch with HIP treatment and a batch without HIP facilitates the surface-based fatigue effect study of this post-treatment process. It shows that the applied HIP treatment does not achieve any benefits in high cycle fatigue strength on the surface layer, because porosities within the surface layer are not completely closed and especially micropores close to the surface can enforce an increase in surface notch factor. This surface-based effects of HIP on aluminum castings lead to a decrease in fatigue strength, which is oppositional to the known benefits in volumetric fatigue strength by HIP treatment due to reduction of micropores. Summing up, the manufacturing process of aluminum castings including optional post-treatment processes such as HIP ought to be evaluated separately for volumetric and surface strength to distinct between these effects properly.