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.

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Frequently Asked Questions

Technical questions on alkali metal behaviour in aluminium melts and when removal flux is needed.

The main problematic alkali metals in aluminium melts are sodium, calcium, and lithium. Sodium causes over-modification of the Al-Si eutectic, inter-granular corrosion in Al-Mg alloys, and increased oxide film formation. Calcium forms calcium aluminide intermetallics that create hard inclusions and promotes sludge in high-iron alloys. Lithium promotes hydrogen absorption and oxide film formation. Elevated alkali levels are most common in secondary aluminium operations processing mixed-source scrap, where these elements can accumulate from contaminated charge materials.

Alkali removal flux is worked into the molten aluminium by plunging and stirring, bringing the reactive flux components into contact with dissolved alkali metals throughout the bath. The flux reacts with dissolved sodium, calcium, and lithium to form stable compounds — typically chlorides or oxides — that are insoluble in the aluminium melt and float to the surface as part of the dross layer. This dross is skimmed from the bath, taking the reacted alkali compounds with it and reducing the alkali level in the remaining melt.

Sodium-free and calcium-free covering fluxes are preventive — they stop new sodium or calcium entering the melt via the flux. Alkali removal flux is a corrective treatment used when alkali metals are already present above specification, typically from scrap contamination, refractory leaching, or accumulated residues. Both types may be used in the same operation: alkali removal flux to treat an out-of-spec heat, followed by sodium-free or calcium-free covering flux to prevent further alkali pick-up during the holding and pouring cycle.

CFC Egypt manufactures EGYFLUX 610 and EGYFLUX 645 for alkali removal from aluminium melts. Both are reactive flux formulations designed to be worked into the melt to reduce dissolved sodium, calcium, and lithium concentrations. Contact CFC for guidance on which product suits your specific alkali contamination profile, required removal level, furnace type, and alloy grade.

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Related Flux Categories

Other CFC aluminium flux types addressing alloy chemistry control and melt contamination.

Aluminium Treatment

Sodium-Free Flux

Covering and drossing flux formulated without sodium compounds for sodium-sensitive alloys.

Aluminium Treatment

Demagging Flux

Reactive flux that reduces excess magnesium content in the aluminium melt.

Aluminium Treatment

Sodium & Calcium-Free Fluxes

Specialist covering fluxes excluding both sodium and calcium compounds.

All Types

Aluminium Treatment Overview

Browse all twelve aluminium treatment product categories from CFC Egypt.

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Dealing with elevated alkali levels in your aluminium melt?

Tell us your alloy grade, current alkali analysis, furnace type, and target chemistry limits. Our technical team will recommend the appropriate EGYFLUX alkali removal product, treatment procedure, and dosing rate to bring your melt back within specification.

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