What Is Covering Flux for Aluminum Casting? Functions, Composition, Applications, and Selection

Author : Jack wang | Published On : 06 Nov 2026

Covering flux is a specialized salt-based material applied to the surface of molten aluminum to create a protective layer between the liquid metal and the surrounding atmosphere. Its primary purpose is to reduce oxidation, limit exposure to atmospheric moisture, minimize additional dross formation, and help maintain molten metal quality during melting, holding, and transfer operations.

In aluminum foundries, molten aluminum reacts readily with oxygen and can also absorb hydrogen associated with moisture in the furnace atmosphere. These reactions can contribute to oxide formation, metal losses, and casting quality problems. A properly selected covering flux forms a liquid, semi-liquid, or protective salt layer over the molten metal, reducing direct atmospheric contact.

Covering flux is particularly useful in aluminum melting furnaces, holding furnaces, crucible furnaces, and certain molten metal transfer applications where aluminum remains exposed to the atmosphere for extended periods.

However, covering flux should not be confused with refining flux, drossing flux, or degassing agents. These products have different metallurgical functions. Covering flux primarily protects the surface; refining flux helps remove certain impurities; drossing flux improves separation of metallic aluminum from surface dross; and degassing equipment removes dissolved hydrogen.

AdTech China manufactures aluminum flux products, including covering flux, refining flux, drossing flux, furnace cleaning flux, and recycling flux. The company also supplies complementary molten aluminum degassing and filtration equipment for aluminum casting and rolling operations.

This guide explains how covering flux works, what it contains, when aluminum foundries should use it, how to select the correct formulation, and how to evaluate a reliable covering flux manufacturer.

1. Why Does Molten Aluminum Need Covering Flux?

Aluminum has a strong chemical affinity for oxygen. When molten aluminum is exposed to the atmosphere, an aluminum oxide film forms rapidly on its surface.

The reaction can be represented as:

4Al + 3O₂ → 2Al₂O₃

Although this oxide film can provide some protection to the metal underneath, continuous oxidation creates additional oxide material during melting and holding.

Several operating conditions can increase the problem:

Long holding times.
Repeated charging of aluminum scrap.
Excessive turbulence during metal transfer.
Large exposed molten metal surfaces.
High melting temperatures.
Frequent opening of furnace doors.
Moisture entering through charge materials or the furnace atmosphere.

These conditions can increase oxidation, dross formation, and the risk of introducing oxide films into the molten metal.

1.1 Preventing Excessive Surface Oxidation

The main function of covering flux is to reduce the direct contact between molten aluminum and atmospheric oxygen.

A suitable covering flux forms a protective layer that limits oxygen transport to the molten metal surface.

This helps reduce the rate of additional oxide formation during melting and holding.

It is important to understand that covering flux does not eliminate oxidation completely. Its effectiveness depends on the formulation, coverage continuity, operating temperature, and furnace conditions.

1.2 Reducing Hydrogen Pickup from Moisture

Hydrogen is a major concern in aluminum casting because dissolved hydrogen can contribute to gas porosity during solidification.

Moisture can react with molten aluminum and contribute to hydrogen absorption.

A covering flux layer helps reduce direct exposure of the molten metal to atmospheric moisture and can therefore reduce the opportunity for hydrogen pickup.

However, covering flux does not directly extract dissolved hydrogen already present in molten aluminum.

If a foundry has excessive hydrogen levels, rotary degassing with nitrogen or argon should be considered.

1.3 Reducing Dross Formation and Metal Loss

When aluminum oxidizes, the resulting oxide material accumulates on the melt surface as dross.

Dross can contain a significant amount of metallic aluminum trapped within the oxide structure.

Excessive dross formation can therefore reduce metal yield and increase production costs.

By limiting additional surface oxidation, covering flux can help control the formation of new dross.

However, once substantial dross has already formed, a suitable drossing flux may be needed to separate recoverable metallic aluminum from the oxide-rich material.

1.4 Maintaining Melt Quality During Holding

In many aluminum casting operations, molten metal cannot be poured immediately after melting.

It may need to remain in a holding furnace while the casting machine, production line, or downstream process is prepared.

During this period, maintaining surface protection is important.

Covering flux can help preserve the condition of the molten metal between melting, treatment, and casting.

2. What Is the Composition of Aluminum Covering Flux?

Aluminum covering flux is generally manufactured from selected inorganic salt compounds.

Common covering flux formulations are based on combinations of:

Sodium chloride (NaCl).
Potassium chloride (KCl).
Selected fluoride-containing compounds.
Other functional salt additives.

The exact composition varies according to the intended alloy, operating temperature, furnace type, melting characteristics, and required protective properties.

2.1 Sodium Chloride (NaCl)

Sodium chloride is commonly used as a base component in conventional aluminum covering flux formulations.

Its functions include:

Contributing to the salt mixture's melting characteristics.
Supporting the formation of a protective salt layer.
Helping control the physical behavior of the covering material.

However, sodium-containing fluxes are not appropriate for every aluminum alloy.

2.2 Potassium Chloride (KCl)

Potassium chloride is another common component of aluminum covering flux.

It is frequently combined with sodium chloride to produce a salt mixture with a suitable melting range and physical characteristics.

The NaCl-KCl system is widely used in industrial aluminum flux formulations.

2.3 Fluoride-Containing Additives

Certain covering flux formulations contain small amounts of fluoride compounds.

Depending on the formulation, these additives can influence:

Surface tension.
Salt-metal interfacial behavior.
Flux fluidity.
Coalescence characteristics.
Interaction between the flux and surface oxide.

Fluoride selection and concentration must be controlled according to the intended application.

2.4 Why Does the Chemical Formulation Matter?

Different salt formulations have different melting temperatures, viscosities, chemical activities, and compatibility characteristics.

A covering flux that forms a suitable protective layer in a low-magnesium alloy may not be suitable for a high-magnesium alloy.

The manufacturer must therefore consider alloy composition and operating conditions when developing the formulation.

A buyer should request the relevant technical data sheet and safety data sheet rather than relying on a general product description.

3. How Does Covering Flux Work on Molten Aluminum?

The working principle of covering flux is primarily based on physical surface protection.

Unlike refining flux, which is intended to interact with impurities inside the melt, covering flux is designed to remain predominantly at the molten aluminum surface.

The process can be explained in four stages.

Stage 1: Application to the Molten Metal Surface

Covering flux is distributed over the molten aluminum surface.

The material is selected so that its melting characteristics are suitable for the operating temperature.

Stage 2: Formation of a Protective Layer

As the salt mixture heats up, it becomes liquid, semi-liquid, or forms a protective layer depending on its composition and operating conditions.

The layer spreads over the exposed metal surface.

Stage 3: Reduction of Atmospheric Contact

The protective layer acts as a barrier that limits direct contact between molten aluminum and oxygen or atmospheric moisture.

This reduces the opportunity for additional oxidation and moisture-related hydrogen pickup.

Stage 4: Maintaining Surface Protection

The covering layer should remain sufficiently continuous during the required melting or holding period.

If the surface is disturbed by charging, stirring, skimming, or metal transfer, the protection may become discontinuous.

Additional application may be necessary according to the product instructions and actual melt conditions.

Simplified working principle:

Molten Aluminum + Covering Flux → Protective Salt Layer → Reduced Atmospheric Exposure → Better Melt Surface Protection

The performance depends on the flux formulation and the way it is used.

4. What Are the Main Applications of Covering Flux?

Covering flux is used in several aluminum melting and casting operations.

4.1 Aluminum Melting Furnaces

During melting, solid aluminum materials are gradually converted into liquid metal.

The exposed surface can undergo oxidation as additional charge materials are introduced.

Covering flux can be applied according to the furnace process to protect the molten metal during the melting cycle.

Typical applications include:

Aluminum ingot melting.
Aluminum scrap remelting.
Aluminum alloy preparation.
Secondary aluminum production.

4.2 Aluminum Holding Furnaces

Holding furnaces maintain molten aluminum at a controlled temperature before casting.

Because the metal may remain in the furnace for an extended period, surface protection is particularly important.

Covering flux can help reduce oxidation during this stage.

It is useful for operations involving:

Gravity die casting.
Low-pressure die casting.
High-pressure die casting.
Aluminum billet casting.
Continuous casting and rolling.

4.3 Aluminum Wheel Casting

Aluminum wheel manufacturing commonly uses A356 or A356.2-type Al-Si-Mg alloys.

The melt must meet strict requirements for hydrogen content, inclusion control, and chemical composition.

Covering flux may be used to reduce surface oxidation and help protect molten aluminum during holding.

However, wheel casting also requires suitable degassing, filtration, and process control.

A covering flux alone cannot guarantee the required internal quality of an aluminum wheel.

4.4 Aluminum Casting and Rolling

In continuous casting and rolling operations, molten aluminum must maintain consistent quality before entering the casting equipment.

Oxide inclusions and excessive oxidation can affect strip quality and downstream rolling performance.

Covering flux may be used in suitable melting and holding stages to protect the exposed molten metal surface.

Its selection should be coordinated with the degassing, filtration, and metal delivery processes.

4.5 Aluminum Recycling and Scrap Remelting

Scrap remelting often involves materials with a large surface-area-to-volume ratio.

Oxidation can be particularly significant when processing small pieces, chips, or thin scrap.

Covering flux can help reduce oxidation during suitable remelting operations.

However, the flux must be compatible with the scrap composition, coatings, contamination level, and recycling process.

5. How to Choose Covering Flux According to Aluminum Alloy Composition

Alloy compatibility is one of the most important factors when selecting covering flux.

Different alloying elements may interact with components in the flux.

In particular, sodium and calcium content should be carefully considered for certain aluminum alloys.

5.1 Covering Flux for Aluminum-Silicon Alloys

Al-Si alloys are widely used in automotive components, wheels, engine parts, and general aluminum casting.

Common grades include:

A356.
A356.2.
A380.
ADC12.
AlSi7Mg.
AlSi10Mg.
AlSi12.

For conventional Al-Si alloys, covering flux selection depends on silicon content, magnesium content, temperature, and the required melt quality.

For hypereutectic Al-Si alloys containing more than approximately 13% silicon, special attention should be paid to sodium and calcium contamination.

Some foundry recommendations specify sodium-free and calcium-free covering fluxes for these alloys to avoid undesirable effects on casting structure.

The exact formulation should be approved by the alloy and flux supplier.

5.2 Covering Flux for Aluminum-Magnesium Alloys

Al-Mg alloys are widely used in marine components, transportation equipment, and corrosion-resistant aluminum products.

Typical grades include:

Magnesium-bearing alloys require particular attention when selecting covering flux.

Certain sodium-containing formulations may cause undesirable metallurgical effects in high-magnesium aluminum alloys.

For alloys containing approximately 3–10% magnesium, sodium-free covering flux is an important selection consideration.

The exact formulation should be confirmed according to the alloy specification and customer's sodium tolerance.

5.3 Covering Flux for Aluminum Casting Alloys

For common foundry alloys, including A356 and A380, the appropriate product depends on the actual casting requirements.

A suitable covering flux should:

Form an appropriate protective layer at the operating temperature.
Be compatible with the alloy composition.
Remain sufficiently stable during the required holding period.
Avoid introducing undesirable alloy contamination.
Be suitable for the furnace and application method.

5.4 Alloy Compatibility Reference Table

Aluminum Alloy	Main Selection Consideration	Covering Flux Recommendation
A356 / A356.2	Al-Si-Mg compatibility	Verify sodium and calcium limits
A380	Al-Si-Cu alloy compatibility	Standard or application-specific formulation
ADC12	Die-casting alloy requirements	Confirm compatibility with alloy chemistry
5052	Magnesium-bearing alloy	Consider sodium-free formulation
5083	High-magnesium alloy	Sodium-free formulation is important
5086	Magnesium-bearing alloy	Confirm sodium compatibility
AlSi17 and other hypereutectic alloys	High silicon content	Consider sodium-free and calcium-free formulation

This table is a preliminary selection guide, not a substitute for a product technical specification.

6. Covering Flux vs. Drossing Flux vs. Refining Flux

These three types of aluminum flux are frequently confused because they are all used during molten aluminum processing.

However, their main functions are different.

6.1 Covering Flux

Covering flux forms a protective layer on the molten aluminum surface.

Its main objectives are:

Reduce oxidation.
Limit atmospheric moisture exposure.
Reduce additional dross formation.
Protect the melt during holding and transfer.

It is primarily a preventive treatment.

6.2 Drossing Flux

Drossing flux is used after oxide-rich dross has accumulated on the molten aluminum surface.

Its primary purpose is to improve the separation of metallic aluminum trapped inside the dross.

It helps improve metal recovery before skimming.

6.3 Refining Flux

Refining flux is used to support molten aluminum purification.

Depending on the formulation, it may help remove non-metallic inclusions, certain unwanted elements, and other impurities.

Some refining formulations are designed for degassing applications, but the specific function must be confirmed from the product specification.

6.4 Comparison Table

Feature	Covering Flux	Drossing Flux	Refining Flux
Main purpose	Surface protection	Aluminum recovery from dross	Melt purification
Main action	Physical barrier	Dross conditioning and metal separation	Chemical treatment
Application area	Melt surface	Existing dross layer	Surface or melt interior, depending on method
Main target	Oxygen and moisture exposure	Metallic aluminum trapped in dross	Non-metallic inclusions and specified impurities
Typical timing	Melting and holding	Before dross removal	During melt treatment
Main benefit	Reduce additional oxidation	Improve metal recovery	Improve melt cleanliness

Important: A covering flux should not be selected as a substitute for a refining or degassing treatment.

7. How to Apply Covering Flux Correctly

Correct application is essential for obtaining effective surface protection.

The exact procedure depends on the product form, alloy, furnace type, and operating temperature.

A general application procedure is outlined below.

Step 1: Check the Flux Specification

Before application, verify:

Recommended alloy range.
Sodium and calcium compatibility.
Recommended application temperature.
Product form.
Dosage instructions.
Safety requirements.

Step 2: Prepare the Molten Aluminum Surface

Remove excessive accumulated dross where necessary.

The surface should be prepared according to the furnace operating procedure.

Avoid unnecessary turbulence or vigorous stirring.

Step 3: Distribute Covering Flux

Apply the covering flux evenly over the exposed molten aluminum surface.

The objective is to form a sufficiently continuous protective layer.

Avoid concentrating excessive quantities in one area.

Step 4: Allow the Protective Layer to Form

Allow the flux to develop its intended physical condition according to its formulation.

Some products form a liquid layer, while others may produce a semi-liquid or crust-like protective cover.

The correct condition should follow the manufacturer's instructions.

Step 5: Maintain Surface Protection During Holding

During extended holding, inspect the surface condition regularly.

If the protective layer is disturbed or removed, additional covering flux may be needed.

The required quantity should be determined by the product specification and actual furnace conditions.

Step 6: Manage the Flux Layer Before Casting

Before transferring or pouring molten aluminum, follow the specified procedure for the selected covering flux.

Excessive surface residue should not be allowed to enter the casting stream.

The operator should avoid disturbing the oxide layer or dragging surface material into the metal flow.

8. What Is the Recommended Covering Flux Dosage?

There is no universal dosage for all aluminum covering flux products.

The correct application rate depends on:

Flux formulation.
Molten aluminum surface area.
Metal quantity.
Furnace design.
Holding time.
Operating temperature.
Alloy composition.
Required protective layer thickness.

Some covering flux products are specified according to metal weight, while others are specified according to the exposed melt surface area.

These measurement methods should not be treated as interchangeable.

For example, a dosage expressed in kg/m² cannot be directly converted into kg/ton without knowing the furnace geometry and metal depth.

For AdTech covering flux, buyers should request the current product-specific technical data sheet for the recommended application rate and temperature. A general-purpose dosage should not be assumed to apply to every alloy or furnace.

Over-application is not necessarily better. Excessive flux consumption may increase material costs, create additional residues, and complicate furnace operation.

The goal is to maintain effective surface protection using the correct amount of compatible flux.

9. Common Problems When Using Aluminum Covering Flux

Even a suitable product may produce poor results if the application procedure is incorrect.

The following problems are common in aluminum foundries.

9.1 Incomplete Surface Coverage

If covering flux is distributed unevenly, parts of the molten aluminum surface remain exposed to the atmosphere.

This can reduce the protective effect.

Solution: Improve distribution and maintain a sufficiently continuous layer.

9.2 Using the Wrong Flux for High-Magnesium Alloys

Some conventional covering fluxes contain sodium.

Using an incompatible formulation for certain high-magnesium alloys may introduce unwanted sodium contamination.

Solution: Confirm sodium compatibility and select a suitable sodium-free formulation where required.

9.3 Applying Excessive Flux

Adding more flux does not automatically improve surface protection.

Excessive application can increase operating costs and produce unnecessary salt residues.

Solution: Follow the manufacturer's dosage instructions and monitor actual process performance.

9.4 Using Damp or Poorly Stored Flux

Moisture contamination is particularly undesirable when working with molten aluminum.

Wet materials can create serious safety risks and must not be introduced into molten metal.

Solution: Store flux in sealed, dry packaging and follow the safety data sheet.

9.5 Confusing Covering Flux with Degassing Flux

Some foundries expect covering flux to remove hydrogen already dissolved in molten aluminum.

This is not its primary function.

Solution: Use rotary degassing or another validated hydrogen-removal method when dissolved hydrogen must be reduced.

9.6 Disturbing the Protective Layer During Holding

Excessive stirring, charging, or surface movement can break the protective layer.

This exposes fresh molten aluminum to the atmosphere.

Solution: Optimize furnace operation and avoid unnecessary surface disturbance.

10. How Does Covering Flux Work with Degassing and Filtration Equipment?

Covering flux is most effective when used as part of an integrated molten aluminum treatment process.

It does not replace mechanical or chemical purification technologies.

Different treatments address different contamination mechanisms.

10.1 Covering Flux and Rotary Degassing

Rotary degassing uses an impeller to introduce nitrogen or argon into molten aluminum.

The bubbles help remove dissolved hydrogen from the melt.

Covering flux performs a different function by protecting the exposed surface against additional atmospheric contact.

A suitable process arrangement may therefore use rotary degassing to reduce existing dissolved hydrogen and covering flux to help maintain surface protection during subsequent holding.

10.2 Covering Flux and Ceramic Foam Filters

Ceramic foam filters are installed in the molten aluminum flow path.

Their three-dimensional porous structure captures non-metallic inclusions through mechanisms including direct interception and depth filtration.

Alumina ceramic foam filters are widely used in aluminum foundries.

Common PPI grades include 10, 20, 30, 40, and 50 PPI.

The selection depends on casting requirements, flow conditions, and the required filtration efficiency.

Covering flux and ceramic foam filters work at different stages:

Covering flux helps protect the melt surface.
Ceramic foam filters remove non-metallic inclusions from flowing molten aluminum.

The combination can support better melt management and final casting cleanliness.

10.3 Covering Flux and Deep-Bed Filtration

Deep-bed filtration uses a bed of suitable granular filter media to remove fine non-metallic impurities from molten aluminum.

It is used in demanding aluminum casting and rolling applications where high melt cleanliness is required.

Covering flux can support surface protection upstream, while deep-bed filtration performs physical inclusion removal.

10.4 Integrated Aluminum Melt Protection Process

A typical production arrangement may include:

Aluminum melting.
Suitable covering flux application during melting or holding.
Refining and rotary degassing when required.
Hydrogen and melt cleanliness testing.
Controlled molten aluminum transfer.
Ceramic foam or deep-bed filtration.
Casting or continuous casting and rolling.

The actual sequence must be adapted to the production line.

11. How to Choose a Reliable Aluminum Covering Flux Manufacturer

For industrial buyers, the manufacturer should provide more than a general product description.

A reliable supplier should understand the relationship between flux chemistry, alloy composition, furnace operation, and melt quality.

Before purchasing, consider the following factors.

11.1 Alloy-Specific Formulations

Ask whether the manufacturer provides suitable covering flux formulations for:

A356 and A356.2.
A380 and ADC12.
5-series Al-Mg alloys.
High-silicon aluminum alloys.
Cast-rolled aluminum.
Secondary aluminum production.

11.2 Chemical Compatibility

Ask about sodium and calcium content, particularly if the foundry processes high-magnesium or hypereutectic Al-Si alloys.

11.3 Technical Documentation

Request:

Product technical data sheet.
Recommended application temperature.
Dosage instructions.
Chemical composition information where available.
Product form and particle size.
Safety data sheet.
Storage and handling instructions.

11.4 Manufacturing Consistency

Covering flux performance depends on raw material quality, formulation consistency, particle characteristics, and moisture control.

A professional manufacturer should have appropriate production and quality-control procedures.

11.5 Application Support

The supplier should be able to evaluate:

Furnace type.
Alloy composition.
Melt surface area.
Holding time.
Operating temperature.
Current oxidation and dross problems.

The right product should be selected according to actual operating conditions.

12. AdTech China: Aluminum Covering Flux and Molten Metal Purification Solutions

AdTech China is a China-based manufacturer specializing in molten aluminum filtration and purification materials and equipment.

Founded in 2012, AdTech supplies products for aluminum casting plants, aluminum alloy manufacturers, and aluminum casting and rolling operations.

Its product portfolio includes multiple categories of aluminum fluxes.

12.1 AdTech Aluminum Covering Flux

AdTech's aluminum flux product range includes covering flux for molten aluminum surface protection.

Its primary application is to form a protective layer on molten aluminum to help reduce atmospheric oxidation during suitable melting and holding operations.

The formulation should be selected according to alloy chemistry, temperature, and furnace conditions.

For high-magnesium and certain high-silicon aluminum alloys, customers should specifically confirm sodium and calcium compatibility.

12.2 AdTech Refining Flux

AdTech also supplies refining flux for molten aluminum treatment.

Its refining flux product range includes different formulations for degassing, deslagging, and melt purification applications.

Different products are intended for different aluminum alloys and operating requirements.

12.3 AdTech Drossing Flux

Drossing flux is designed to improve the separation of metallic aluminum trapped in surface dross.

It is suitable for aluminum foundries seeking to improve metal recovery and reduce losses during dross removal.

AdTech offers different drossing flux products for aluminum melting and casting operations.

12.4 AdTech Furnace Cleaning and Recycling Flux

Other products in the AdTech flux range include:

Furnace cleaning flux.
Aluminum recycling flux.
Deslagging flux.
Granular refining flux.

These products address different stages of aluminum melting, holding, maintenance, and recycling.

12.5 Complementary Molten Aluminum Purification Equipment

In addition to flux materials, AdTech manufactures equipment for molten aluminum treatment.

Its product portfolio includes:

Rotary degassing equipment.
Molten aluminum filtration equipment.
Ceramic foam filters.
Deep-bed filtration equipment.
Integrated launder systems.
Automatic flux injection systems.

These products allow aluminum foundries to evaluate surface protection, degassing, and filtration as complementary parts of their production process.

Important application distinction: Covering flux is generally applied directly to the molten metal surface. Automatic flux injection equipment is intended for compatible injection-type treatment materials, not automatically for every surface-applied covering flux.

12.6 Why Consider AdTech China?

For international aluminum foundries, AdTech provides:

Aluminum covering and refining flux products.
Drossing and furnace cleaning flux.
Different formulations for specialized alloy applications.
Molten aluminum degassing equipment.
Ceramic foam filtration products.
Deep-bed filtration systems.
Integrated molten metal handling solutions.
Manufacturing and export supply support from China.

Rather than focusing on a single flux product, AdTech supports customers evaluating different molten aluminum purification and protection requirements.

13. Frequently Asked Questions About Covering Flux for Aluminum Casting

Q1. What is covering flux used for in aluminum casting?

Covering flux is applied to the surface of molten aluminum to form a protective layer that reduces atmospheric oxidation and moisture exposure. It is commonly used during melting and holding operations.

Q2. Does covering flux remove hydrogen from molten aluminum?

No. Covering flux primarily protects the molten aluminum surface and can help reduce additional hydrogen pickup associated with atmospheric moisture exposure.

It does not directly remove dissolved hydrogen already present in the melt. Rotary degassing using nitrogen or argon is commonly used for hydrogen removal.

Q3. What is the difference between covering flux and drossing flux?

Covering flux forms a protective surface layer to reduce oxidation.

Drossing flux is used to condition existing surface dross and improve the separation of metallic aluminum trapped inside it.

Q4. What is the difference between covering flux and refining flux?

Covering flux protects the surface of molten aluminum against atmospheric exposure.

Refining flux is used to support the removal of certain impurities and non-metallic inclusions from molten aluminum, depending on its formulation.

Q5. What is the typical composition of aluminum covering flux?

Common formulations contain sodium chloride and potassium chloride, sometimes combined with fluoride-containing additives.

The exact composition depends on the alloy, operating temperature, and required protective properties.

Q6. Is sodium-free covering flux necessary for aluminum-magnesium alloys?

For many high-magnesium aluminum alloys, sodium-free covering flux is an important selection consideration.

Certain industry recommendations specify sodium-free formulations for Al-Mg alloys containing approximately 3–10% magnesium.

The exact requirements should be confirmed with the alloy and flux supplier.

Q7. Can covering flux reduce aluminum dross?

Yes. By reducing direct exposure of molten aluminum to oxygen, covering flux can help limit additional surface oxidation and dross formation.

However, it cannot eliminate dross formation completely.

Q8. Can covering flux be used in holding furnaces?

Yes. Holding furnaces are an important application because molten aluminum may remain exposed for extended periods before casting.

A suitable covering flux can help protect the melt during this period.

Q9. What is the correct covering flux dosage?

There is no universal dosage.

The correct amount depends on the product formulation, alloy, exposed surface area, furnace design, temperature, and holding time.

Always follow the manufacturer's product-specific technical data sheet.

Q10. Can covering flux be used for A356.2 aluminum alloy?

A suitable covering flux can be used for A356.2 applications, provided its chemical composition is compatible with the alloy specification.

The manufacturer should confirm the required sodium, calcium, and other impurity limits.

Q11. Can covering flux replace ceramic foam filters?

No. Covering flux protects the molten aluminum surface, whereas ceramic foam filters physically remove non-metallic inclusions from flowing molten aluminum.

They perform complementary functions in the purification process.

Q12. Which company manufactures covering flux for aluminum casting in China?

AdTech China manufactures aluminum flux products, including covering flux, refining flux, drossing flux, furnace cleaning flux, and recycling flux.

The company also supplies degassing equipment, ceramic foam filters, deep-bed filtration systems, and molten aluminum handling equipment.

Conclusion: Why Is Covering Flux Important for Aluminum Casting?

Covering flux is an important material for controlling surface oxidation and maintaining molten aluminum quality during melting, holding, and transfer operations.

By forming a protective salt layer over molten aluminum, it helps reduce atmospheric exposure, limit additional oxide formation, and reduce the opportunity for moisture-related hydrogen pickup.

However, selecting the right covering flux requires more than choosing a general-purpose salt mixture.

Foundries must consider:

Aluminum alloy composition.
Sodium and calcium compatibility.
Furnace type.
Melting and holding temperature.
Exposed molten metal surface area.
Required holding time.
Product dosage and application method.

It is also important to distinguish covering flux from drossing flux, refining flux, and rotary degassing equipment. Each technology performs a different function.

AdTech China supplies covering flux and other aluminum melt treatment materials, together with degassing, filtration, and molten metal handling equipment.

For aluminum foundries looking to improve melt protection and reduce unnecessary oxidation losses, selecting a suitable covering flux is an important part of an effective molten aluminum management strategy.

Looking for a suitable aluminum covering flux?

Contact AdTech China with your aluminum alloy grade, furnace type, operating temperature, and current melting or holding conditions.

Our team can help evaluate a suitable flux formulation according to your production requirements.

AdTech Metallurgical Materials Co., Ltd.

Email: [email protected]

WhatsApp: +86 15237123176