Research progress on flame-retardant methods for magnesium alloys

Due to the high-temperature oxidation and flammability characteristics of magnesium alloys, flame-retardant technology is indispensable for both the melting of magnesium alloys and the research and development of high-temperature magnesium alloys. This paper provides an overview of the high-temperature oxidation behavior and mechanisms of magnesium alloys. It then systematically reviews the mechanisms and research progress of the three primary flame-retardant methods: the flux flame-retardant method, the gas flame-retardant method, and the alloying flame-retardant method. To address the environmental concerns associated with the flux flame-retardant method, current research introduces auxiliary components such as carbonates and inorganic compounds into the covering flux, thereby effectively reducing emissions of toxic gases including HCl, Cl₂, and HF. Research on the gas flame-retardant method focuses on gaseous components such as fluoroalkanes and hydrocarbon derivatives. These gases promote the formation of a dense oxide film, which improves the film’s thermal stability and flame-retardant performance. The core of the alloying flame-retardant method lies in the fact that the addition of rare earth elements can significantly improve the structure and stability of the oxide film. However, the mechanisms of existing alloying flame-retardant method at the atomic level remain insufficiently studied. Future research should integrate high-resolution characterization techniques with computational approaches such as thermodynamic calculations (e.g., CALPHAD) to predict stable oxide phases, first-principles calculations (e.g., density functional theory) to elucidate oxygen adsorption and diffusion pathways, and molecular dynamics or phase-field simulations to model oxide film growth and failure mechanisms across multiple scales. This combined strategy will enable a comprehensive understanding of the structure, evolution, and oxidation mechanisms of magnesium alloy oxide films. Furthermore, the addition of costly rare earth elements during the melting of magnesium alloys leads to losses of these elements and significantly increases melting costs. Therefore, there is an urgent need for in-depth development of high-temperature magnesium alloys based on composite rare-earth flame-retardant systems, as well as research into their adaptability for industrial applications. This is essential to promote the widespread use of magnesium alloys in aerospace, 3C, and other fields.