Microstructure, microsegregation, and mechanical properties of directional solidified Mg-3.0Nd-1.5Gd alloy

The microstructure, microsegregation, and mechanical properties of directional solidified Mg-3.0Nd-1.5Gd ternary alloys were experimentally studied. Experimental results showed that the solidification microstructure was composed of dendrite primary α(Mg) phase and interdendritic α(Mg) + Mg₁₂(Nd, Gd) eutectic and Mg₅Gd phase. The primary dendrite arm spacing λ₁ and secondary dendrite arm spacing λ₂ were found to be depended on the cooling rate R in the form λ₁ = 8.0415 × 10^-6 R^-0.279 and λ₂ = 6.8883 × 10^-6 R^-0.205, respectively, under the constant temperature gradient of 40 K/mm and in the region of cooling rates from 0.4 to 4 K/s. The concentration profiles of Nd and Gd elements calculated by Scheil model were found to be deviated from the ones measured by EPMA to varying degrees, due to ignorance of the back diffusion of the solutes Nd and Gd within α(Mg) matrix. And microsegregation of Gd depended more on the growth rate, compared with Nd microsegregation. The directionally solidified experimental alloy exhibited higher strength than the non-directionally solidified alloy, and the tensile strength of the directionally solidified experimental alloy was improved, while the corresponding elongation decreased with the increase of growth rate.