Oxidation and Ignition Behaviors of Molten Mg-Nd-Zr Alloy in Resin-Sand Mold

High-temperature oxidation behavior of molten Mg-Nd-Zr in the pyrolysis atmosphere of resin-bind sand mold was investigated. The results showed that pouring temperature higher than 1023 K would sharply increase the ignition risk of melt in mold. The oxide formed on Mg-Nd-Zr melt below 973 K consists of two layers: mainly MgO for outer layer; mixture of MgO and Nd2O3 for inner layer. The inner oxide mixture layer played an essential role in the protection of Mg-Nd-Zr matrix. Based on the experimental results and thermodynamic analysis, the oxidation process containing three stages was proposed. Nd- and Zn-enriched zone was found at the subsurface of oxide scale, without the enrichment of Zr. DICTRA calculation results indicated that this phenomenon was caused by the depletion of Mg and up-hill diffusion of Zr. Thus, Zr showed limited protection to the melt in long-term oxidation.

研究了在树脂砂型热解气氛中熔融Mg - Nd - Zr的高温氧化行为。结果表明，浇注温度高于1023 K会大幅增加熔体在铸型中的着火风险。在973 K以下，Mg - Nd - Zr熔体上形成的氧化物由两层组成：外层主要为MgO；内层为MgO和Nd₂O₃的混合物。内层氧化物混合层对Mg - Nd - Zr基体的保护起着至关重要的作用。基于实验结果和热力学分析，提出了包含三个阶段的氧化过程。在氧化皮的次表面发现了富Nd和富Zn区，而没有Zr的富集。DICTRA计算结果表明，这种现象是由Mg的消耗和Zr的上坡扩散引起的。因此，Zr在长期氧化过程中对熔体的保护作用有限。