Research On Corrosion And Protection Of Mild Steel Used To Make Crucible For Magnesium Alloy Melting

Crucible is one of the main smelting units for the melting magnesium and its alloy. The crucible is generally made of carbon steel at present. However the iron-based crucible was easily eroded and oxidized by high temperature magnesium alloy liquid, agent of fusion and protective gas, it not only shortened the operational life of the crucible, but also debased the quality of magnesium alloy. The subject investigated of this research was low carbon steel which was made as melting magnesium alloy crucible. The performance of low carbon steel crucible, used to melt magnesium alloy, was investigated. The composite coating on the surface of aluminized steel was made by high-temperature reaction. The relationship between the thickness and technological parameter was analyzed. The microstructures and composition of the layer were investigated by means of optical microscope and X-ray Diffraction (XRD). Protection of the coating was study by immersing the coating samples in AZ91 alloy liquid wholly. Three main characters of the coating were tested, including heated shock resistance, high temperature oxidation resistance and agent of fusion corrosion resistance. The conclusions were as follows:(1) The target materials, such as TiB₂ and MgO, which were selected by calculating of thermodynamic feasibility, have good stability and didn't react with magnesium alloy liquid.(2) The relationship between the thickness of coating and two processes parameters ( reaction temperature and holding time ) were investigated by metallographic analysis. The result showed that the coating which was made of transition layer and outer layer was tightly combined with the substrates. The thickness of coating increased when the reaction temperature and holding time grew. The layer was consisted of TiB₂, MgO, Mg₂TiO₄, Mg₂B₂O₅, Fe3Al, FeAl and Ti₂B₅.(3) It showed that the coating could protect ferroalloy crucible from being...