USE OF SO2/AIR/N2 COVER GASES FOR THE PROTECTION ON MOLTEN MAGNESIUM AND AZ91D ALLOY
WANG Xianfei, XIONG Shoumei()
State Key Laboratory of Automotive Safety and Energy, School of Materials Science and Engineering, Tsinghua University, Beijing 100084
Cite this article:
WANG Xianfei, XIONG Shoumei. USE OF SO2/AIR/N2 COVER GASES FOR THE PROTECTION ON MOLTEN MAGNESIUM AND AZ91D ALLOY. Acta Metall Sin, 2014, 50(1): 32-40.
Molten magnesium and AZ91D alloy oxidize rapidly during casting process, sulfur dioxide (SO2) mixed with carrier gases can be used to protect the melt by reacting with the melt to form a coherent protective film on the melt surface. In this work, the films formed in SO2/Air/N2 cover gases were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), the formation process and the protective mechanism of the surface film were also discussed. The results show that the protective film is composed of MgO, MgS and MgSO4. MgS increases the pilling and bedworth ratio of the surface film and enhances its protective capability. MgSO4 is the thermodynamically stable phase and its formation is important for the formation of protective film. When SO2/Air/N2 cover gases are used to protect the melt and SO2 content is fixed, air content should be controlled within a certain range.
Fund: Supported by National Natural Science Foundation of China (No.51275269), National Key Technologies R&D Program (No.2011BAE22B02) and International S&T Cooperation Program of China (No.2010DFA72760)