Aluminium Treatment — Degassing

Degassing Flux

Degassing flux for aluminium is a powder flux that, when spread across or plunged into the molten bath, releases fine gas bubbles that scavenge dissolved hydrogen from the aluminium melt as they rise through it — reducing hydrogen content before pouring and minimising the gas porosity that is the most common internal defect in aluminium castings.

Liquid aluminium absorbs hydrogen from atmospheric moisture and combustion products at elevated temperature; when the metal solidifies, the excess hydrogen precipitates as gas bubbles — gas porosity — that reduces mechanical properties, causes pressure-tight castings to leak, and creates voids exposed by machining. CFC Egypt's EGYFLUX 400 degassing flux powder is applied before each pour, generating gas bubbles that scavenge dissolved hydrogen throughout the bath as they rise. For large reverberatory and induction furnaces where powder coverage of a large bath area is practical, EGYFLUX 400 is the economical choice; for smaller furnaces and crucible operations, the tablet form (EGYHEX AL) provides precise metered dosing from a plunged position at bath depth.

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Where Degassing Flux Is Used

Aluminium degassing is required before pouring wherever gas porosity would cause quality failures in the casting — pressure testing, x-ray inspection, mechanical property requirements, or machining surface quality.

Pressure-Tight Castings — Hydraulic & Pneumatic Components

Pump housings, valve bodies, and hydraulic manifolds cast in aluminium must be free of gas porosity to pass pressure testing — typically hydrostatic pressure tests to 2 to 5 times operating pressure. Even small gas pores interconnected through the casting wall create leak paths. Degassing before each pour is the primary process control for achieving the low hydrogen content needed to produce pressure-tight aluminium castings consistently.

X-Ray Inspected Aerospace & Automotive Castings

Aerospace and safety-critical automotive castings are radiographically inspected to acceptance criteria such as ASTM E155 or equivalent, which define maximum permissible pore sizes and distributions. Gas porosity that exceeds these limits causes the casting to be scrapped or downgraded. Consistent degassing before each pour reduces gas pore population and size, improving the proportion of castings passing x-ray inspection at first attempt.

Sand & Shell Casting — Hydrogen Control

In sand and shell castings, gas cannot easily escape through the mould face during solidification, making pre-pour degassing the only effective control for gas porosity. Sand-cast aluminium components for marine, oil and gas, and power generation applications frequently require both degassing and low-porosity quality documentation. EGYFLUX 400 applied before each ladle or direct furnace pour keeps hydrogen below the threshold for visible porosity in these applications.

Heat-Treated & T6-Processed Castings

Aluminium castings subjected to solution heat treatment (T4 or T6) at temperatures above 480°C are vulnerable to blistering — the growth of sub-surface gas pores to visible blisters on the casting surface — if hydrogen content is too high. This is the mechanism behind HPDC casting blisters after T6 treatment. Degassing before pouring, whether by flux powder or tablets, reduces hydrogen to the level where T6 heat treatment does not cause blistering.

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CFC Degassing Flux Product

EGYFLUX 400 — degassing flux powder for aluminium, releasing gas bubbles throughout the bath to scavenge dissolved hydrogen before pouring.

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Frequently Asked Questions

Technical questions on hydrogen in aluminium melts and how degassing flux reduces it.

Liquid aluminium absorbs hydrogen readily from moisture in the furnace atmosphere, humid charge materials, wet tools, and hydrocarbon combustion products. Hydrogen dissolves into the liquid metal at elevated temperature because its solubility in liquid aluminium is significantly higher than in solid aluminium. When the metal solidifies, the solubility drops sharply and the excess hydrogen precipitates as gas bubbles — forming gas porosity within the casting. Gas porosity reduces mechanical strength, causes failure in pressure-tight castings, and produces sub-surface voids that open up during machining.

Degassing flux powder is spread across the melt surface or plunged below it. The flux reacts at temperature to release gas in the form of fine bubbles rising through the bath. These bubbles have a low hydrogen partial pressure, which drives dissolved hydrogen from the surrounding aluminium into the bubble by diffusion. The bubbles carry the hydrogen to the surface where it is released into the furnace atmosphere. The number and size of bubbles generated, their distribution through the bath depth, and contact time all determine degassing efficiency.

Degassing flux should be applied after the melt is fully liquid and at temperature, after covering and drossing treatment but before pouring. Degassing too early — before the melt is fully liquid or at temperature — reduces effectiveness. Degassing too late — just before pouring with no time for dross removal — may leave surface contamination. The standard sequence is: melt fully liquid, flux and skim for covering and drossing, degas, skim lightly, pour. For large furnaces, repeated treatments may be needed over a long holding period to maintain low hydrogen levels.

Degassing flux powder (EGYFLUX 400) is spread or plunged into the melt — suited to large open-bath reverberatory and induction furnaces where broad coverage of the bath surface is practical. Degassing tablets (EGYHEX AL) are pre-measured compact tablets plunged to the furnace floor on a steel rod, releasing gas in a controlled metered way from depth. Tablets are preferred for smaller furnaces, crucible melters, and ladles where precise dosing matters and the operator benefits from lower fume compared with surface powder spreading.

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Related Aluminium Treatment Products

Other CFC products that complement degassing flux in the aluminium treatment cycle.

Aluminium Treatment

Degassing Flux

Powder flux that removes dissolved hydrogen from the melt before pouring, reducing gas porosity.

Aluminium Treatment

High-Pressure Die Casting Flux

HPDC-specific flux for holding furnaces, complementing degassing as part of full melt quality control.

Aluminium Treatment

Covering, Drossing & Cleaning Fluxes

Multi-function flux powders and granules for melt surface protection and metal recovery.

All Types

Aluminium Treatment Overview

Browse all twelve aluminium treatment product categories from CFC Egypt.

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Need to reduce gas porosity in your aluminium castings?

Tell us your furnace type, alloy grade, casting process, and current porosity challenges. Our technical team will recommend EGYFLUX 400 or EGYHEX AL tablets, dosing rate, and treatment timing to reduce hydrogen to the level required for your casting quality specification.

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