Six alloys were prepared by high pressure die casting in order to develop a magnesium secondary alloy system for mixed post-consumer scrap. The alloys were investigated with regard to intermetallic phases, grain structures, mechanical properties and performance in the salt spray test. The results are discussed in relation to the characteristics of the high pressure die casting process. The effect of contamination by copper and compensation for this effect by the addition of zinc were thoroughly investigated for the most promising alloy. It is evident that the alloying elements strontium, silicon and calcium are incorporated in the ternary Zintl phase Sr_6.33Mg_16.67Si₁₃, while aluminium, zinc, copper and magnesium form the tau-phases Mg₃₂(Al_x,Cu_1−x)₄₉ and Mg₃₂(Al,Zn)₄₉. The two tau-phases can merge due to isomorphism. Mg₃₂(Al,Zn)₄₉ ensures improved corrosion resistance after the addition of copper.