New magnesium-tin-calcium alloys offer the potential to improve the property profile and to extend the range of applications for magnesium alloys. Alloy development is undertaken in accordance to the formation of intermetallic phases during casting or during subsequent heat treatment. These intermetallic phases may contribute to room temperature strength as well as to the improvement of creep properties. Therefore the behaviour and the structure of these phases needs to be understood in more detail when using these materials in the as-cast condition or after subsequent heat treatment.