Aluminium Treatment — Demagging
Demagging Flux
Demagging flux is a reactive aluminium flux used to reduce the dissolved magnesium content of an aluminium melt that has exceeded alloy specification limits — converting excess Mg to a skimmable slag compound and restoring the melt to its target chemistry before pouring, preventing hot shortness and porosity in the resulting castings.
Excess magnesium in an aluminium melt arises most often in secondary operations when high-Mg scrap alloys are mixed with lower-Mg target grades, resulting in a heat with Mg above specification. At elevated Mg levels, aluminium die casting alloys exhibit hot shortness — cracks forming in the casting during ejection — and gravity casting alloys show increased porosity and surface roughness. CFC Egypt's EGYFLUX 100 (demagging flux) is worked into the melt by plunging and stirring, where it reacts with dissolved magnesium to form magnesium compounds that float to the surface as slag for skimming. The treatment brings the Mg level back within specification, salvaging a heat that would otherwise need to be diluted with low-Mg primary metal or scrapped entirely.
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Where Demagging Flux Is Required
Demagging is a corrective treatment for aluminium heats where magnesium has exceeded the alloy specification — most commonly in secondary aluminium and recycling operations.
Secondary Aluminium — Variable Scrap Composition
The most common use of demagging flux is in secondary aluminium operations where the scrap input contains a higher proportion of Al-Mg alloys than planned — 5xxx wrought scrap, Al-Mg gravity casting returns, or unidentified mixed scrap. When the bath sample comes back with Mg above the target alloy specification, demagging flux treatment corrects the heat before it is poured or cast, avoiding the production of non-conforming material.
High-Pressure Die Casting — Preventing Hot Shortness
HPDC alloys such as EN AC-46000 (Al Si9 Cu3) are formulated with Mg below 0.55% for a reason: elevated Mg causes hot shortness — the tendency of the casting to crack during ejection from the die while still hot. Hot shortness results in scrap castings, damaged tooling, and production stoppages. Demagging flux treatment of the holding furnace metal when Mg is found to be above specification prevents these quality and downtime consequences.
Alloy Grade Switching — Heel Metal Management
When switching furnace production between alloy grades — for example, from an Al-Mg alloy to a lower-Mg die casting alloy — residual heel metal in the furnace contains elevated Mg from the previous charge. Rather than waiting for the Mg to dilute through multiple charges (at the cost of out-spec metal), demagging flux treatment of the heel reduces the Mg to a level compatible with the next alloy, accelerating grade transition and minimising the quantity of off-spec transition metal produced.