Magnesium fading

The fading of magnesium is primarily a consequence of the oxidation and evaporation. Oxidation can be seen as oxygen contact. The causes for this include:

  • Lower oxides, i.e. instable towards magnesium, in the slag
  • Slag formations in the ladle
  • Oxygen in the pores of the refractory lining
  • Contact of the melt with the atmosphere etc.

The reaction of the dispersed slag particles in the melt with atmospheric oxygen plays an important role in this. Typcial for such reactions is the formation of MgS. MgS particles rise to the bath surfaced where they react with oxygen from the air. MgO occurs, sulfur is released, diffuses back into the melt and triggers re-sulfurization. The released sulfur atoms bond with Mg to MgS and are oxidized back on the bath surface. The casting result can be optimized by the degree of pureness of the melt, correct choice of the refractory material and correct choice of the casting method (s. Magnesium treatment). Last but not least, this also has a significant influence on the stability of the magnesium adjustment and fading.

The handling of treated melts can speed up magnesium fading. The following mechanisms can be made responsible for triggering this behavior: Turbulences occur during recasting which increase the contact surface between the melt and the atmosphere - they contribute to the coagulation and precipitation of non-metallic inclusions from the melt. According to I. Henych and K. Regitz, the magnesium losses measured in practice are between 0.007 and 0.1% Mg per process.

Additional references:
Fading effect
Magnesium yield
Magnesium residual content
Magnesium treatment wire