Aluminium Treatment — Alkali Removal
Fluxes for Alkali Removal
Alkali removal fluxes are reactive flux formulations worked into the molten aluminium to reduce dissolved alkali metal concentrations — sodium (Na), calcium (Ca), and lithium (Li) — that accumulate from scrap contamination or refractory leaching and cause porosity, oxide structure degradation, and loss of mechanical properties in the cast product.
Elevated alkali levels in aluminium melts are most common in secondary operations processing mixed-source scrap, where sodium, calcium, and lithium may be present in the input material at above-spec concentrations. Alkali metals dissolved in the melt increase oxide film formation, promote hydrogen absorption, and in sodium-modified Al-Si alloys cause over-modification and eutectic coarsening. CFC Egypt's EGYFLUX 610 and EGYFLUX 645 are formulated to react with dissolved alkali metals and transfer them to the dross layer for skimming removal, correcting an out-of-spec heat and returning the melt to alloy chemistry specification before pouring.
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Where Alkali Removal Is Required
Alkali removal flux is a corrective melt treatment used when dissolved alkali metal levels exceed alloy specification limits before pouring.
Secondary Aluminium Remelting — Mixed Scrap Input
Mixed-source aluminium scrap — automotive shredded material, consumer product scrap, industrial process waste — can contain significant quantities of sodium (from flux residues on previous dross), calcium (from flux contamination or alloy carry-over), and lithium (from lithium-containing alloy scrap or lubricants). When this scrap is melted without pre-sorting, the resulting melt may exceed alloy alkali limits and require active treatment before it can be poured to specification.
Al-Si Alloys — Controlling Over-Modification
In Al-Si foundry alloys, sodium modifies the eutectic silicon morphology to improve ductility and strength. When sodium accumulates above the optimal window — from recycled modified alloy, flux residues, or multiple modification additions — the alloy becomes over-modified, exhibiting coarse eutectic and reduced mechanical properties. Alkali removal flux can reduce sodium to the target range before re-modification at the correct level, salvaging a heat that would otherwise require dilution.
Wrought Aluminium — Chemistry Correction Before Casting
Wrought aluminium billet and slab casters operating against tight customer chemistry specifications use alkali removal flux as a last-resort treatment when melt sampling before casting shows alkali levels above the specification limit. Active alkali removal — combined with degassing — can bring the heat back within specification, avoiding the cost of scrapping or diluting a full furnace charge.
Remelting Lithium-Containing Alloy Scrap
As Al-Li alloys become more common in aerospace structures, their scrap re-enters the secondary aluminium stream. Lithium in the melt is particularly problematic because it is a strong oxide former and promotes hydrogen absorption. Alkali removal flux applied before pouring can reduce lithium to acceptable levels, enabling secondary aluminium producers to recycle Al-Li-contaminated scrap into standard casting or wrought alloy grades without producing off-spec product.
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CFC Alkali Removal Flux Products
EGYFLUX 610 and EGYFLUX 645 — reactive flux formulations for reducing dissolved sodium, calcium, and lithium in aluminium melts, manufactured in Sadat City, Egypt.
EGYFLUX 645
Retardateur de prise et superplastifiant pour béton (ASTM C-494 - Type A, D & G)