Melt treatment agents

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Melt treatment agents (until the middle of the 20th century generally referred to as flux, melting salt or melting agent) are additives that are used when melting metals and alloys ( melt treatment ).

Purposes of melt treatment

They are more diverse than the terminology used earlier suggests. The only thing that is the same for each type of treatment is that it has to remove undesirable properties from the melt and impart desirable ones. This also includes the addition and removal of elements, be it oxidizing and slagging the oxides formed, be it by adding in the form of master alloys or suitable salt mixtures. Flux , a term that goes beyond metallurgy, is only used correctly in the context of melt treatment for recycling melts.

Melt treatment agents play an important role in the metallurgy of ferrous and non-ferrous metals, in the latter case this applies in particular to alloys of aluminum and magnesium, furthermore to all alloys based on copper, as well as all other common alloys of non-ferrous metals, whether they are based on zinc, tin, or Lead.

Use with copper-based alloys

Melting with the base metal copper tends to oxidize and absorb hydrogen, which leads to blistered castings which are defective due to oxide inclusions . Melt treatment agents enable perfect metal quality with appropriate furnace operation by first removing the hydrogen by oxidation and then reducing the remaining oxygen to a tolerable level by deoxidation or even slightly overcompensating it (phosphorus deoxidation ). In this way, flawless castings can be produced in the absence of technical defects.

Use with aluminum-based alloys

The situation is more complex with aluminum and especially its most common alloys based on aluminum- magnesium or aluminum-silicon. With all alloys, the particularly undesirable dissolved hydrogen must be removed by chemical or mechanical rinsing treatment ( impeller ). Since the solubility for hydrogen in an aluminum melt is significantly higher than in the solidified state, porosity of the cast parts is the result. In addition, all of the oxidic particles of the gamma and alpha type (the latter better known as hard corundum ) and spinels from oxides of aluminum and magnesium that float in the easily oxidizable melt, some of which are very fine, must be removed as they lead to strength-reducing inclusions in the castings .

In addition, additives such as sodium or strontium are used to refine (influence the structure) of aluminum-silicon alloys, which are widely used in automotive engineering . They lead to a significantly firmer structure. In addition, a grain refinement treatment (influencing the structure) can improve the strength and resilience of the castings. This is usually the case with aluminum-magnesium alloys. Additions of titanium and boron , including zirconium, are common . They are supplied as so-called master alloys or powdered or pelletized additives from salts that release the desired element in the melt.

See also

literature

  • Foundry glossary. Schiele & Schön, Berlin
  • Foundry practice. No. 1-1, 1977.
  • Aluminum. P. 473/476, Aluminum-Verlag, Düsseldorf, 1989.
  • VDG leaflet R 50. "Melt treatment agents for non-ferrous metals and alloys"
  • The FOSECO Foundryman's Handbook. Pergamon Press

Footnotes

  1. Foundry Practice. No. 1-2, 1977.