Regulation mechanism of Y on surface adsorption of MgO/Y2O3 and cooperative heterogeneous nucleation in shear-remelted recycled Mg-5Y alloy

To address the bottleneck of partial yttrium (Y) burn-off and the formation of coarse oxide inclusions during the remelting and regeneration of Mg-5Y, high-shear melt conditioning (HSMC) process was adopted to decompose the chain-like Y 2 O 3 and large particles of MgO into dispersed micro-nano particles, resulting in a dense and radiating grain refinement. First-principles calculations revealed that the lattice mismatch between Y 2 O 3 (100) and α-Mg (0001) was only 7.9%, and the terminal interfacial energy of Y 2 O 3 was as low as −1.763 J/m 2 , confirming the efficient heterogeneous nucleation substrate characteristics of Y 2 O 3 . The Y atom preferentially adsorbs on the surfaces of MgO (111) and Y 2 O 3 (100), occupying the energetically optimal F sites on most surfaces, and its adsorption energy is always significantly higher than that of the Mg atom. Moreover, the co-adsorption of Y and Mg increased the adsorption energy of Mg atoms by 0.11- 0.34 eV. The electronic structure analysis further revealed that Y strengthened the Mg-Mg bonds and Mg-Y bonds through charge transfer and orbital hybridization, significantly promoting the nucleation of Mg. The enrichment of Y simultaneously increased the undercooling and reduced the interfacial energy, and the combined effect of cooperatively reduced the nucleation barrier, promoting the heterogeneous nucleation of α-Mg and achieving a significant refinement of the Mg-5Y alloy grains.