High quality recycling of WE54 alloy machining chips via synergistic high shear melt conditioning and controlled diffusion solidification

High-quality remelting and recycling of Mg-5Y-4Nd (WE54) alloy machining chips were achieved through the synergistic application of high shear melt conditioning (HSMC) and controlled diffusion solidification (CDS). The solidification microstructure of the conventionally remelted chips consists of coarse, elongated oxide inclusions and the Mg 12 Nd phase. These coarse oxide inclusions severely fragment the matrix and tend to induce stress concentration, thereby deteriorating the mechanical properties of the recycled alloy. After the HSMC treatment, the oxide inclusions are refined, leading to a recovery in the mechanical properties of the recycled alloy. However, its strength remains inferior to that of the original alloy, which is primarily attributed to the loss of Y in the matrix. To compensate for the Y depletion, the HSMC-treated Nd-rich melt (high-temperature, low-mass) was mixed with a Mg-25Y melt (low-temperature, high-mass) via CDS. This successfully replenished Y and induced the re-precipitation of a β-Mg 14 Nd 2 Y phase, which was finer than that in the original alloy due to the growth-restricting pinning effect of Y 2 O 3 and MgO. Additionally, the grain size of the recycled alloy is refined by ∼43% compared to the original alloy, owing to the highly efficient heterogeneous nucleation promoted by the dispersed oxide inclusions during the CDS process. Benefiting from these microstructural improvements, the recycled alloy prepared via the HSMC-CDS route exhibits a simultaneous enhancement in strength and ductility. Compared to the original alloy, the yield strength and ultimate tensile strength of the recycled alloy are increased by ∼34.6% and 45.8%, respectively, with a ∼52.4% improvement in elongation.