Magnesium alloys of the rare earth metals: systematics and properties

Recent literature data on the possible technological beneficial effects of the addition of rare earth metals (Rj to magnesium based alloys are briefly reported.The constitutional properties (crystallochemistry; thermodynamics, phase equilibriaj of binary R-Mg alloys are reviewed, subdividing the different groups of systems as the following: those given by the light R, those formed by the heavy R (to which yttrium has to be added) and by scandium and finally the systems with the "divalent" rare earths, europium and ytterbium which show a number of analogies with the typical divalent alkaline earth metals).Properties and characteristics of the Mg-rich alloys are especially described and discussed (Mg solid solutions, stoichiometries and structures, stable and metastable equilibria corresponding to the Mg-richest phases). Several properties of R-Mg alloys change smoothly as a function of the atomic dimension of the trivalent rare earth: similar dependence is also observed in ternary R'-R"-Mg alloys, formed by two different trivalent rare earth metals, for which the averaged radius of the R'-R" mixture involved may be used as the corresponding reference parameter. This allows a semi­quantitative check of the reliability of a given R-Mg system and can be used as a first criterion for predicting phase stoichiometries, crystallochemistry and properties of selected ternary alloys in order to design and plan their structures and characteristics