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本文研究了用含SF_6气体做为熔炼镁合金的防燃气相的理论和实践的问题。表面膜的x射线分析结果表明,SF_6参与了表面膜的形成。合金表面膜的基本成分在空气及SF_6气氛中为 MgO+MgF_2;在CO_2+SF_6气氛中为MgO+MgF_2+无定型碳。表面膜中MgF_2的含量在一定范围内随SF_6的浓度和温度的升高而增多。热分析天平测定的氧化曲线表明,在干燥的空气+SF_6气氛中,当SF_6的浓度在1％～0.01％(体积百分比,以下同)范围内,试样的氧化增重随时间的变化曲线为抛物线,表面膜是致密的,具有保护性。当 SF_6的浓度小于0.01％或大于1％时,氧化增重曲线是直线,表面膜是非保护性的。在CO_2+SF_6气氛中,当SF_6浓度小于1％时氧化增重量不大,而且几乎不因合金种类和温度的不同而发生变化。气相中水总是使氧化加剧。合金元素对镁的氧化有一定影响,氧化速度按ZM-1、ZM-5、纯镁和ZM-2的次序变化。
This paper studies the problem of the theory and practice of using gas containing SF_6 as the gas-proof gas phase of smelting magnesium alloy. X-ray analysis of the surface film shows that SF 6 participates in the formation of the surface film. The basic composition of the alloy surface film is MgO + MgF_2 in air and SF_6 atmosphere, and MgO + MgF_2 + amorphous carbon in CO_2 + SF_6 atmosphere. The content of MgF_2 in the surface film increased with the concentration and temperature of SF_6 in a certain range. Oxidation curves measured by the thermal analysis balance showed that the curve of oxidation weight gain of the sample with time in the range of 1% ~ 0.01% (volume percentage, the same below) in the dry air + SF_6 atmosphere is Parabolic, the surface film is dense, protective. When the concentration of SF_6 is less than 0.01% or more than 1%, the oxidation weight gain curve is a straight line, the surface film is not protective. In the atmosphere of CO_2 + SF_6, when the concentration of SF_6 is less than 1%, the weight gain of oxidation is not large, and almost does not change due to the type of alloy and temperature. Water in the gas phase always aggravates the oxidation. Alloying elements have some effect on the oxidation of magnesium, the oxidation rate changes according to the order of ZM-1, ZM-5, pure magnesium and ZM-2.