Oxide Film Structure on Aluminum Alloy 6000 Series Cylindrical Ingot Surface

Electron microscopy and energy dispersion analysis are used to reveal structural features of an oxide film in the region of white deposit areas that are visually detected on the surface of cylindrical ingots of 6000 series aluminum alloy after homogenizing annealing. It is shown that a loose film of aluminum and magnesium oxides with an anomalously high Mg content (up to 45 at.%) and micropores are typical for these areas. Diffusion flow of magnesium towards the surface during homogenizing annealing gives rise to its chemical potential gradient occurring as a result of oxidation processes occurring during annealing. Reasons are determined for the occurrence of white deposit areas connected with formation at an ingot surface of mineral salt oxides and organic compounds from dried liquid used for cooling during ingot semi-continuous casting.