In an effort to gain insight into more unusual magnesium casting alloys an investigation of the binary Mg-Sn and ternary Mg-Sn-Al systems has been undertaken. For initial investigations, permanent mould castings have been made. A range of alloys has been prepared, and the effect of the alloying additions on the microstructure, hardness and corrosion properties studied. Specimens were examined in three heat treatment conditions: as-cast (F), solution heat treated and aged (T6) and artificially aged only (T5).