THE INTERGRANULAR MICROSTRUCTURE OF CAST MG-ZN AND MG-ZN-RARE EARTH ALLOYS

The solidification path and microstructure of cast Mg-9Zn and Mg-8Zn-1 .5MM (misch metal) alloys have been investigated by a combination of t hermal analysis and analytical electron microscopy. The addition of 1. 5 wt pct MM had a strong influence on the as-cast microstructure with the introduction of new ''ternary'' interdendritic phases and structur al modification of known binary phases. The temperature ranges for for mation of these phases from the melt were identified, their crystal st ructures determined, and their compositions analyzed. Products from eu tectoidal decomposition of the interdendritic phase in the binary Mg-9 Zn alloy were also identified.