An enrichment of trace elements and their resulting interactions influence the properties of light-metal alloys increasingly negative. This effect is massively amplified by the high degree of recycling of Aluminum and the global alloy and scrap trade. Therefore, it is essential to measure and interpret the effects of trace elements on the formation of intermetallic phases of Al-casting alloys. The present work deals with the thermodynamic calculation of the influence of trace elements on the formation of intermetallic phases of eutectic Al-cast alloys and their detection in practical experiments. For this investigation three series of samples of an Al Si7Mg0.3 - cast alloy were studied with varying degrees of impurities. The focus of this investigation is on the following trace elements such as Calcium Ca, Titanium Ti, Vanadium V and Zirconium Zr. As measurement methods were used the thermodynamic calculation by Thermo-Calc, thermal analysis, metallographic investigation (LIMI, SEM) and the spectral analysis. The first part of this thesis deals with the thermodynamic calculations of the alloys (high purity, technical purity). The chemical compositions of the mentioned trace elements are correspondingly varied and compared with the results. In the presence of calcium the formation of the Al2Si2Ca-phase is always observed and at higher Levels of Ca primary precipitates can be detected. Furthermore calcium has a refining effect on the Al-Si eutectic. With the addition of Titanium, Vanadium and Zirconium the formation of Al3M (Ti, V, Zr) phases is favoured. In the second part, a comparison between the thermodynamic calculation and a practical castings is made. This demonstrates the sensitivity and validity of the thermodynamic calculation of phases.