A novel flame retardant strategy for molten magnesium alloys: The effect of the new protective gas C3H2F6 on EV33 alloy

Abstract

Resolving the ignition issue of magnesium alloys is essential for broadening their application scope. This research investigates the EV33 magnesium alloy, delving into an innovative flame-retardant strategy, with a specific focus on the impact of the novel protective gas C₃H₂F₆ on the flame-retardant properties of the alloy. This paper unveils the morphological characteristics of the EV33 magnesium alloy surface in the absence of protective gas, while employing thermodynamic principles to establish the preferential reaction stages of the alloy, computing the residual stress of MgF₂, and assessing the flame-retardant and antioxidative properties of C₃H₂F₆. The study finds that under conditions without protective gas, the oxide film on the EV33 alloy surface is prone to cracking, which accelerates the ignition process of the alloy. Conversely, in an environment enriched with C₃H₂F₆, the formation of a dense oxide film on the alloy surface significantly enhances its thermal stability and flame-retardant properties. This mechanism encompasses the formation of a secondary oxide film, where C₃H₂F₆ accelerates the rapid development of this film, effectively repairing damage to the primary oxide film and inhibiting further diffusion of the oxidation reaction. Furthermore, this study elucidates the origin of oxide film rupture, showing that under conditions without protective gas, the precipitated phases and grain boundaries on the surface of the alloy induce the rupture of the oxide film, attributed to stress concentration phenomena occurring around the grain boundaries.