Experimental Investigation of the Mg-Nd-Zn Isothermal Section at 300 °C

The Mg-Nd-Zn isothermal section at 300 degrees C was established in the full composition range using diffusion couples and equilibrated key alloys. Microstructural characterization was carried out using WDS, XRD, and metallographic methods. The homogeneity ranges of the binary and ternary compounds were determined by WDS analysis. Six ternary compounds were observed in the Mg-Nd-Zn system at 300 degrees C. These are: tau(1) (Nd5Mg21+xZn45-x; 0 <= x <= 4), tau(2) (Nd5Mg3+yZn25-y; 0 <= y <= 1), tau(3) (NdMg1+zZn2-z; 0 <= z <= 0.44), tau(4) (Mg40Nd5Zn55), tau(5) (Mg22-23.5Nd15.5-17.5Zn59.1-61.8), and tau(6) (Nd-2(Mg,Zn)(23)). tau(5) was found to have a homogeneity range of 22.0-23.5 atom % Mg, 15.5-17.6 atom % Nd and 59.1-61.8 atom % Zn and tau(6) was found to have 54.1-61.3 atom % Mg at a constant Nd of 8.0 atom %. The ternary solubility of Zn in Mg-Nd compounds was found to increase with the decrease in Mg concentration. Accordingly, (Mg41Nd5) was found to have an extended solubility of 3.1 atom % Zn, whereas (Mg3Nd) was found to have 30.0 atom % Zn. MgNd was found to have a complete substitution of Mg by Zn. The maximum solid solubility of Zn in alpha-Mg was measured as 4.8 atom % Zn.