Rare metals and rare earth metals additions to aluminum alloys can have potential benefits in mechanical and technological properties during alloy development. The aim of this study is to evaluate the influence of selected rare metals and rare earth metals to aluminum alloys on the solidification behaviour. Furthermore, effects and fundamental mechanisms were be analyzed. In addition to a theoretic assessment of the impact of rare (earth) metals in general, special emphasis is given to the elements tantalum and scandium. In a comprehensive study experimental examinations were performed with minor rare (earth) metal additions in aluminum-copper-, aluminum-magnesium- and aluminum-magnesium-silicon-alloys for die casting and high pressure die casting. The results indicate that the solidification behaviour is essential for the achieved properties. Tantalum additions cause the precipitation of the Al3(Ta)-phase. In combination with other transition metals other tantalum-phases are formed. Furthermore, tantalum has a large growth restriction in aluminum, a small grain size and therefore improvements in ductility and strength are obtained. The addition of scandium caused the precipitation of the Al3Sc-phase. The growth restriction parameter for scandium in aluminum is too low. The achieved fine grain results from excellent nucleation of the α-aluminum on the Al3Sc-phase and vice versa by an epitaxial orientation relationship with extreme small lattice misfit. At fast cooling rates (high pressure die casting) scandium misaligns the solidification morphology from a dendritic to a globular morphology by a reduction of the local concentration difference and therefore a reduction of the constitutional undercooling responsible for interfacial stability.