How to Clean Aluminum for Industrial Welding

The integrity of a weld is highly dependent on surface preparation. Aluminum has a natural tendency to form oxide and even a thin layer can lead to weld defects. Oxide and potential contamination from oils, lubricants, paints, and particulate matter can create bubbles of air trapped inside the materials, impacting the bonding process. 

One of the reasons aluminum is a popular material is because of its corrosion resistance. When the oxide layer forms, it acts as a protective barrier.

However, when oxides penetrate the welds, it leads to increased porosity and accelerates deterioration — impacting the bond strength of adhesives and reducing strength and durability.

There are various methods for cleaning aluminum. Depending on the operation and application, there are five commonly used methods of cleaning before welding aluminum.

Table of Contents

• Quick comparison table
• 1. Laser cleaning
• 2. Chemical cleaning
• 3. Mechanical abrasion
• 4. Solvent degreasing
• 5. Plasma cleaning

Quick comparison table

1. Laser Cleaning

Laser cleaning employs a high-powered laser to ablate and vaporize surface contaminants without physically contacting the material. The laser, guided by a high-speed scanner and focusing lens, delivers intense energy to the surface to remove oxidation, oils, and other residues with precision. This method is particularly appealing for its environmentally friendly nature, as it generates minimal waste and eliminates the need for chemical handling.

Advantages

• Precise and non-destructive: Laser cleaning removes only the contaminants, leaving the underlying aluminum substrate virtually untouched.
• Consistent results: Laser cleaning offers consistent results, which is essential for automated welding processes. Cleanliness can be validated with RFU (Relative Fluorescence Units) or water contact angle measurements. A small droplet of water on a very clean surface will spread out (low contact angle), while it will bead up on a contaminated surface (high contact angle).
• Real-time monitoring: Integrated sensors can monitor the UV (plasma) and IR (heat) radiation emitted during laser cleaning, providing real-time feedback on the cleaning process. This allows for immediate adjustments and ensures consistent cleaning quality.
• Automation-friendly: Laser cleaning can be easily integrated into automated machines that also measure the emission of radiation to validate the weld’s high quality. Cleaner surfaces lead to more predictable signals and decrease the amount of "false negatives" where the machine incorrectly identifies a weld as bad.

Disadvantages

• Higher upfront costs: The initial investment for laser cleaning equipment may be significant.
• Specialized training: Operating and maintaining laser cleaning systems requires specialized knowledge and training.
• Potential issues: Factors such as laser power and the distance of the object being cleaned need to be calibrated correctly to optimize the cleaning recipe.

Laser cleaning is ideal for applications requiring high precision and minimal surface alteration, such as cleaning aluminum before battery welding, where consistent surface quality is crucial for accurate weld monitoring and validation.

Laser cleaning is also ideal for removing paint and oxidation before welding in situations where masking is undesirable.

2. Chemical Cleaning

Chemical cleaning (pickling) involves the use of alkaline or acidic solutions to dissolve and remove surface contaminants. This method is effective for removing grease, oil, and light oxidation from large surface areas but requires several steps, including pre-cleaning, acid immersion, and inhibitor usage to prevent over-pickling — plus rinsing and neutralization.

Advantages

• Effective for multiple contaminants: Chemical cleaning can remove a variety of contaminants simultaneously.
• Large surface areas: Suitable for cleaning large surface areas quickly.
• Lower equipment costs: The equipment cost for chemical cleaning is relatively low.
• Penetrates irregularities: Chemicals can access and clean small surface imperfections.

Disadvantages

• Environmental and health hazards: Many chemical cleaners pose environmental and health risks.
• Handling and disposal: Requires careful handling, storage, and disposal of chemical solutions.
• Surface damage: Risk of etching or damaging the aluminum surface.
• Residue potential: Potential for chemical residue if not thoroughly rinsed.
• Verification: Requires manual inspection to verify and additional cleaning after the pickling process.

Chemical cleaning is commonly used for pre-treating surfaces before MIG or TIG welding aluminum in industries where large volumes of parts need to be processed quickly. However, it is falling out of favor due to environmental concerns and the hazardous waste it can generate.

3. Mechanical Abrasion

Mechanical abrasion techniques, such as using a stainless steel wire brush or wire wheel, angle grinder, or sandblaster, physically remove surface oxides and contaminants.

Advantages

• Effective on thick oxides: Highly effective at removing thick oxide layers and heavy contamination, which can impact the fusion of filler metal.
• Lower initial cost: Low initial equipment cost compared to laser or plasma cleaning.
• Visual Confirmation: Provides visual confirmation of cleaning effectiveness.
• Versatile: Can be used on a wide range of aluminum alloys and surface conditions.

Disadvantages

• Surface roughness: Can create a rough surface finish, which may not be desirable for certain applications.
• Contamination risk: Potential for introducing surface contamination from the abrasive material or tools. As the cleaning tool deteriorates, it can also transfer contamination from previous uses to the next part being cleaned.
• Labor-intensive: Can be labor-intensive, especially for large or complex aluminum parts.
• Micro-deformations: May cause micro-deformations in the metal surface.
• Uneven preparation: It can be difficult to achieve even surface preparation.

Mechanical abrasion is often used for preparing aluminum surfaces for welding in heavy industrial applications where a rough surface finish is desired for increased weld adhesion. However, there are also additional safety hazards. Aluminum dust is combustible and can pose a health risk if breathed in.

4. Solvent Degreasing

Solvent degreasing involves using specialized solvents to remove hydrocarbons such as oils or grease, and organic contaminants from aluminum surfaces and is often performed before other cleaning methods. There are several different solvents that can be used, including acetone, methyl ethyl ketone (MEK), toluene, and mineral spirits.

Advantages

• Quick removal of contaminants: Quickly removes organic contaminants.
• Non-abrasive: Can be effective for delicate surfaces.
• Pre-cleaning step: Ideal as a pre-cleaning step before other methods.
• Effective on oils and greases: Highly effective at removing oils and greases.

Disadvantages

• Environmental concerns: Many solvents are environmentally harmful.
• Health risks: Potential health risks from solvent exposure.
• Ineffective on oxides: Not effective for removing aluminum oxide layers.
• Ventilation required: Requires proper ventilation to mitigate health risks.
• Limited on heavy contamination: Can be limited in effectiveness on heavy contamination.

Solvent degreasing is widely used in various industries as a preliminary cleaning step to remove oils and greases before further processing or welding. It can also be used to remove paint, which may be preferable to masking.

5. Plasma Cleaning

Plasma cleaning uses ionized gas to remove surface contaminants from aluminum. It is effective for cleaning intricate surfaces and complex geometries without altering their properties and removing contaminants that might interfere with the welding arc and electrodes.

Advantages

• Clean surface: Produces extremely clean aluminum before welding, removing oxy aluminum and impurities
• Complex geometries: Works well on complex geometries.
• No chemical waste: Generates no chemical waste.
• Uniform cleaning: Provides uniform cleaning across the entire surface.

Disadvantages

• High equipment cost: Initial equipment costs can be significant
• Specialized knowledge: Requires specialized training and technical knowledge
• Limited on thick contaminants: Limited effectiveness on very thick layers.
• Material sensitivity: Sensitive to surface material properties.

Plasma cleaning is an option for industries requiring extremely clean surfaces and precise cleaning of complex parts, such as in the aerospace and electronics sectors.

Which one is right for you? The choice depends on the specific application and the balance between cost, cleanliness requirements, volume, and environmental concerns.

If you want to discuss laser as an option for your application, contact us to discuss with an expert.

Let Us Know Your Application

Alex Fraser

With a PhD in Laser Processing, Alex is one of the two laser experts who founded Laserax. He is now Vice President and Chief Technology Officer, overseeing the team that develops laser processes for laser marking, cleaning, texturing, and welding applications.

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