Effects of residual F content in a sealed melting furnace on experimental results of cover gas research for magnesium alloys

The origin, formation and function of residual F in a sealed melting furnace of magnesium alloy were analyzed and discussed. The results showed that residual F content has a very strong influence on the subsequent experimental results of cover gas experiments. The effects last for a long time and are difficult to eliminate. With the increase of the residual F content, the degree of its influence also increases. The residual F element exists in various kinds of fluorides, such as MgF2, FeF2 and FeF3, which are formed by the reactions between the magnesium alloy or the inner wall of the steel furnace and the atmosphere containing the F element. Because of the considerable vapor pressures of Mg2F4, FeF2 and FeF3 at experimental temperatures, MgF2, FeF3 and FeF2 are formed and gradually accumulate on the inner wall of the furnace. These fluorides are gradually changed into gases and deposited on the surface of the magnesium melt or react with the magnesium melt during the process of heating the steel furnace from room temperature to the handling temperature. At the same time, protective surface films were formed on the magnesium melt.