In the 30(th) and 40(th) and also in the late 80(th) of the last century there was a rapid increase in use of magnesium alloys in automotive industry. Magnesium alloy gearbox housings and engine blocks were produced by chill casting, as a result of the relatively low engine temperatures the alloys proved adequate. Development of modem water-cooled engines increased the application temperature and magnesium alloys were replaced by cast iron and aluminium alloys because of the limited strength and creep resistance of magnesium alloys at higher temperatures. At the end of the last century alloy development as well as development of magnesium based metal matrix composites (MMCs) was carried out to improve the high temperature strength and creep resistance. Alloy development occurred in several directions; either the reduction of aluminum and the addition of elements that preferentially combine with aluminum or the complete elimination of aluminum as an alloying element. The need to eliminate or to reduce the aluminum content is because it is known that P phase (Mg17Al12) contributes to the poor creep resistance in aluminum containing alloys. From the aluminum containing magnesium high-pressure-die-casting (HPDC) alloys, AE42 currently shows the best creep properties. This is due to the Al-RE precipitates, which suppress the formation Of Mg17Al12.