In this work, the 450°C Mg-Mn-{Ce, Nd} and 300°C Ce-Mg-Zn isothermal sections were established using diffusion couples and key alloys. The phase relationships were determined using XDR, EDS/WDS and metallography. Diffusion couples were also used to measure the interdiffusion coefficients of the Mg-{Ce, Nd, Zn} and Zn-{Ce, Nd} binary systems based on the experimental composition profiles and Boltzmann-Matano method.
No ternary compounds were found in the Mg-Mn-{Ce, Nd} isothermal sections at 450°C. Microstructures of the ternary diffusion couples showed stationary Mn grain morphology in most of the diffusion zones. This was attributed to the affinity of Ce and Nd to Mg atoms, which forming several Mg-{Ce, Nd} binary compounds during the diffusion process. However, some of these binary compounds dissolved Mn. The ternary solubility of (γ-Ce)Mg,Mn, (CeMg), (CeMg3), (CeMg12), (α-Nd)Mg,Mn, (MgNd) and (Mg3Nd) was measured at 450°C to be 3.0, 5.1, 3.2, 1.8, 3.0, 13.0 and 3.7 at.% Mn, respectively. In both systems, the phase boundary lines were pointing towards the Mn-rich corner, except for the (α-Nd)Mg,Mn+Mn17Nd2+(MgNd) phase field.
Eight ternary compounds were observed in the Ce-Mg-Zn isothermal section at 300°C. These are: τ1 (Ce6Mg3Zn19), τ2 (CeMg29Zn25), τ3 (Ce2Mg3Zn3), τ4 (CeMg3Zn5), τ5
iv
(CeMg7Zn12), τ6 (CeMg2.3-xZn12.8+x; 0≤x≤1.1), τ7 (CeMgZn4) and τ8 (Ce(Mg1-yZny)11); 0.096≤y≤0.43). The ternary solubility of Zn in Ce-Mg compounds was found to increase with the decrease in Mg concentration. Accordingly, the ternary solid solubility of Zn in (CeMg12) and (CeMg3) was measured as 5.6 and 28.4 at.% Zn, respectively.
Diffusion couples with Boltzmann-Matano analysis were used to calculate the interdiffusion coefficients of the Mg-{Ce, Nd, Zn} and Zn-{Ce, Nd} systems. A systematic annealing procedure was followed to obtain all expected phases in the studied systems. For the available literature data for some of the compounds in the Mg-{Ce, Nd, Zn} systems, the calculated interdiffusion coefficients are in good agreement. The activation energy and the pre-exponential factor for the growth of the Mg-{Ce, Nd, Zn} compounds were determined using Arrhenius equation. The activation energies of the growth of the Mg-Ce compounds showed relatively higher values than those of Mg-Nd and Mg-Zn compounds.