Formation of the solid layer on the top of molten aluminum

Abstract

The formation of the top solid layer on the molten aluminum in launders during refining and casting, constituting production loss, were experimentally, thermodynamically and kinetically investigated in the current study. The effects of humidity and composition of the metal on the oxide layer were discussed. The thickness of the top thin oxide layer was only 1 - 5 μm, and the rest of the top layer averaging 350μm were mainly composed of aluminum matrix with MgO clusters, other inclusions and Fe-rich precipitated phases. Two most feasible reactions were determined to be responsible for the formation of the thin oxide layer: (1) the oxidation of molten aluminum by water vapor in humid air and (2) the oxidation of dissolved magnesium by O2. Higher humidity enhanced the oxidation of molten aluminum while lower humidity favored dissolve [Mg] oxidation. Increasing the humidity reduced the thickness of the oxide layer, however, resulted in more hydrogen in the molten metal.