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Surface films that formed on molten AZ91D magnesium alloy in SO_2/air cover gases at 680 ℃ in a sealed furnace were characterized by scanning electron microscopy,energy dispersive spectroscopy,X-ray diffraction and Auger electron spectroscopy.It is revealed that the film formed on molten AZ91 D alloy surface in cover gas with high air content can prevent the molten AZ91 D alloy from oxidation and ignition.The surface film contained three elements,namely magnesium,oxygen and sulfur,and was mainly composed of MgO and MgS.The properties of the film depended on air content in the cover gas and holding time.Thermodynamic calculation showed that MgSO_4 was the stable phase,and it was concluded that the formation of MgSO_4was important for the formation of the protective surface film in SO_2/air atmospheres.
Surface films that formed on molten AZ91D magnesium alloy in SO_2 / air cover gases at 680 ℃ in a sealed furnace were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and Auger electron spectroscopy. It is revealed that the film formed on molten AZ91 D alloy surface in cover gas with high air content can prevent the molten AZ91 D alloy from oxidation and ignition. The surface film contained three elements, namely magnesium, oxygen and sulfur, and was mainly composed of MgO and MgS.The properties of the film depended on air content in the cover gas and holding time. Thermoodynamic calculation showed that MgSO 4 was the stable phase, and it was concluded that the formation of MgSO 4 was important for the formation of the protective surface film in SO 2 / air atmospheres.