Phase relationships in the neodymium-magnesium alloy system

The Nd-Mg system was studied using differential thermal analysis (DTA), X-ray examination, metallography, and microprobe analysis. The following intermetallic compounds were found to exist and their crystal structures confirmed or determined: NdMg (cubic, cP2 CsCl type, melting point 800 \ub0C), NdMg2 (cubic, cF24 MgCu2 type, peritectic formation 3c755 \ub0C), NdMg3 (cubic, cF16 BiF3 type, melting point 780 \ub0C), and Nd5Mg41 (tetragonal, tI92 Ce5Mg41 type, decomposes peritectically at 560 \ub0C). The NdMg2 phase undergoes a eutectoidal decomposition at 660 \ub0C. Three eutectic equilibria were observed to occur at 42.5 at. pct Mg and 775 \ub0C, 64.5 at. pct Mg and 750 \ub0C, and 92.5 at. pct Mg and 545 \ub0C, respectively. In the Nd-rich alloys, previously determined data[15] concerning the Mg solubility in \u3b1-Nd (8.2 at. pct Mg, 48550 \ub0C) were accepted. The Mg solubility in \u3b2-Nd was evaluated as 34 at. pct Mg at 775 \ub0C. The \u3b2-Nd phase was observed to decompose eutectoidally at 17 at. pct Mg and 545 \ub0C. Moreover, in the Mgrich alloys, a metastable NdMg12 phase (tetragonal, tI26 ThMn12 type) was observed in samples quenched from the liquid. The general properties of the Nd-Mg phases are compared with those of the R-Mg compounds and briefly discussed. \ua9 1990 The Metallurgical of Society of AIME