On the systematics of phase equilibria in complex magnesium rare earth systems: Gd-Y-Mg system

General properties of magnesium alloys with one or two different rare earth metals are briefly summarized and discussed. The regular trends observed in the intermediate phase formation are used to predict the characteristics of the room temperature isothermal section of the Gd-Y-Mg system. The partial experimental section at 500 degrees C in the composition range approximate to 50 to 100 at.% Mg, has then been determined and found to be in fair agreement with the predicted one. The determination has been carried out by X-ray powder diffraction, optical and scanning electron microscopy and electron probe microanalysis. The following phases have been identified: the continuous solid solution cP2-CsC1 type along the line Gd1-xYxMg and, along the line Gd1-xYxMg2, two Laves-type solid solution fields (cF24-MgCu2 type, GdMg2 based for about 0 less than or equal to x < 0.18 and hP12-MgZn2 type, YMg2 based for about 0.26 < x less than or equal to 1). The extension into the ternary field, moreover, has been determined for ME and the GdMe3, GdMg5 and Y5Mg24 based phases.