| Magnesium alloy, as the most potential lightweight materials, can easily occur oxidation and combustion under high temperature. Currently, the SF6 with carrying mixture gas like nitrogen is mainly used as flame retardant protection for Mg alloy melt in Magnesium casting industry. However, SF6 will be eliminated due to its high greenhouse effect.Based on the previous research that HFC-125 gas has been confirmed as effective flame protection for magnesium melt, this paper studied HFC-125 gas membrane mechanism and protection effect in contrast with SO2 and SF6 gas, and the influence of HFC-125 and SO2 gas mixture relative concentration on flame retardant protection effect. Meanwhile, the influence of air convection on protection effect and protective ingredients was also practically investigated. In the experiment, the digital cameras were adopted to collect protection effect of each gas. The morphology and composition of the surface film were analyzed by analysis technologies such as scanning electron microscope (SEM),electron spectrum (EDS),X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD).The main results are as follows:â‘ Protection effects1)HFC-125 gas has the same protective effect for magnesium alloy melt as SF6, and they both provide reliable and long-term effective flame protection;2)When HFC-125 protects magnesium melt effectively, air convection condition changing does not affect HFC-125 gas protection effect;3)Adding appropriate amount of SO2 gas in HFC-125 gas can improve HFC-125 gas flame protection for magnesium alloy melt in elevated temperature;â‘¡The morphological features of the surface films1)The same characteristics are presented in the three surface films of magnesium melts by using HFC-125,SF6 and SO2 as gas shield. Namely the protection films are dense-continuous with defects such as drape, crackle and holes, but with no substantial influence on membrane flame retardancy;2)The surface films of HFC-125 and SO2 gas mixture protection of magnesium alloy melt formed under high temperature is flatter than that of SO2 gas protection alone; â‘¢The surface film composition1)When HFC-125 is applied as gas shield, new element F in the surface film is formed in weak air convection condition, while F and O in the surface film are formed in strong air convection condition;2)The new elements F and O are emerged in the surface film of magnesium melt using HFC-125 and SO2 mixed gases protection;3)With the extension of time, the number of atom F increase gradually on the membrane surface formed by HFC-125 gas and HFC-125 and SO2 gas mixture in protecting magnesium melt, while that of Mg decrease.
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