Cast aluminium alloys are commonly used in the automotive industry for casting applications. There are both primary and secondary/recycled aluminium alloys in the market, which differ in price and quality. In this study, the effect of alloy quality on solidification, microstructure and mechanical properties was investigated. The comparison of properties was carried out in the as-cast condition and in the heat-treated condition. The influence of alloy quality on solidification was analysed by simple thermal analysis and differential scanning calorimetry, and thermodynamic simulations. The basic mechanical properties analysed were tensile strength, yield strength, elongation, and hardness. The microstructural differences were analysed using a light microscope. The Mn:Fe ratio, which is strongly influenced by the alloy quality, was found to have a pronounced effect on the mechanical properties, while magnesium together with silicon hardens the aluminium matrix during heat treatment, which significantly increases the mechanical properties. This research proved that thermal analysis methods can give us a necessary and important indication of the quality of the alloys used.