Oxide film

If surfaces of liquid metals and alloys come into contact with atmospheric oxygen, they can be subject to the formation of thin oxide films. The risk of oxide film formation is even higher when the relevant metal or its alloy components exhibit a high degree of oxygen affinity.

Insoluble oxide films are formed during melting, ladle filling and casting, in particular with aluminum, silicon and chromium as well as alloys containing high concentrations of these metals. If these non-metal inclusions penetrate the casting, they disrupt the microstructure and result in the rejection of the casting.

Therefore, oxide inclusions are to be considered as casting defects (Figs. 1 and 2). The most important measures for preventing such defects is to avoid turbulences when filling or transporting ladles and during casting and mold filling, to keep furnaces, crucibles and ladles clean and to carefully clean and skim melts ready for casting.

Additional references:
Oxidation
Oxide inclusion
Casting defect
Mold sand-based casting defect

  • Fig. 1: Oxide film inclusions in the fracture structure, castings made of the alloy AlSi12, not etched, 60:1
  • Fig. 2:  Element spectrum of the inclusion from Fig. 1
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