Study on phase evolution and separation behavior in Gd-containing magnesium alloy scrap recycling by vacuum gasification

High-performance Gd-containing Mg alloys are widely used in aerospace and high-temperature applications, yet conventional recycling processes suffer from significant rare earth loss and low recovery rate, seriously hindering the circular utilization of Mg and strategically valuable Gd. To address this challenge, vacuum gasification technology was employed for the synergistic recovery of Mg and Gd from such scrap, integrating thermodynamic calculations, phase diagram analysis, phase evolution investigations of the Mg-Gd system, and validation experiments on JDM4 alloy scrap. The results demonstrate that vacuum gasification enables effective Mg-Gd separation, with reduced system pressure significantly lowering the required process temperature. Both theoretical and experimental results confirm a consistent phase evolution sequence during separation: Mg₅Gd → Mg₃Gd → Mg₂Gd → MgGd → Gd. During gasification, the Mg-Gd intermetallic compounds exist in a molten state and form a Gd-rich multilayer encapsulated structure, with Gd content increasing from the inside out. This structure inhibits Mg volatilization and induces splashing, leading to Gd loss. Reasonable regulation of the temperature and holding time, the decomposition progression and the state of these encapsulation layers can be effectively managed. Vacuum gasification of JDM4 scrap yielded condensed Mg with a purity of 99.945 wt.% and a Gd product with 93.71 wt.% purity, at recovery rates of 96.61% and 99.91%, respectively. This study provides robust theoretical and practical support for the efficient recycling of Gd-containing magnesium alloys, offering key technical guidance for promoting the sustainable circular economy of Mg and rare earth resources.