How To Glue Aluminium Using Structural Adhesives

Intro to bonding Aluminium

Aluminium is a soft, lightweight metal with good thermal and electrical conductivity, highly regarded for its excellent strength to weight ratio and natural corrosion resistance. It is widely used as a base material in many alloy combinations, and is easily machined, extruded, welded and bonded to using a variety of industrial adhesives to manufacture different products across many industries.

Surface preparation when bonding Aluminium

Surface preparation is essential for achieving a strong, reliable bond when bonding aluminium with industrial adhesives.

Aluminium naturally forms a thin, invisible oxide layer when exposed to air. While adhesives can bond well to this oxide layer, the layer itself can be a weak point which results in poor bond strength or premature bond failure. Some adhesives like our methacrylates can bond structurally with minimal preparation however for best adhesion and where possible it is important to remove this oxide layer.

Preparing the surface of aluminium for bonding with adhesives not only removes the oxide layer but also any oils and surface contaminants in the process which can also cause a weak bond. 

Step 1 - Clean: Clean the aluminium thoroughly using a suitable solvent cleaner that doesn't leave behind residue like Isopropyl Alcohol, Acetone or Nextite Proprep. Even though we will be further treating the surface we want a clean surface to start from without the oils and impurities on the surface. This step alone is not enough to remove the oxide layer.

Step 2 - Abrade: There are a few methods to remove the thin oxide layer on aluminium. We recommend using either an abrasion pad like a scotchbrite pad or sandpaper. Another method is using a grit (sand) blast unit but that sometimes isn't suitable for small - medium scale applications. The scratches and grooves also create more surface area for the adhesive to bond to. 

Step 3 - Clean: Finally, it is important to clean off any residue after abrading the aluminium as you want a good surface for the adhesive to bond to. Use a no residue cleaner like NEXTITE PROPREP, Isopropyl Alcohol, Acetone until there is no contaminants on the bonding surface.

You can see the difference in action with cyanoacrylates (instant adhesives or superglues). Try bonding two pieces of aluminium without any surface preparation, then compare the result with two pieces of prepared aluminium using the steps above. This simple test demonstrates how the oxide layer affects bond strength and  it helps explains the age old question of "why is my superglue not sticking to aluminium?"

Note: some adhesives like methacrylates and MS Polymers can bond to aluminium without much surface preparation and as received (given the substrate is clean). However, where possible for best results and for the highest bond strength it is recommended to clean and abrade aluminium.

What adhesives can bond Aluminium?

Aluminium can be bonded using a variety of industrial adhesives. However, choosing the right adhesive depends on the application, the required bond strength and the materials being joined. Bonding aluminium to itself presents different considerations than bonding it to dissimilar materials such as plastics, composites or other metals. Differences in thermal expansion, flexibility and operating conditions should also be considered to ensure a durable, long-lasting bond.

Methacrylates (MMA)

Strengths	Structural adhesive, bonds dissimilar materials, toughened and flexible bond, fast cure at room temperature, good gap filling, good impact strength, widely used in industry manufacturing, limited surface preparation required although recommended.
Limitations	Generally viscosity is high, stronger odour, exothermic reaction (although limited).
Most Suitable	All NEXTITE methacrylate adhesives bond aluminium structurally. We recommend using NEXTITE AB83x for bonding aluminium to itself and other materials as it offers exceptional strength, toughness, fatigue and impact resistance. Unlike more rigid adhesives, NEXTITE AB83x retains some flexibility after curing, helping accommodate differences in thermal expansion between dissimilar materials.  NEXTITE AB800 Series - NEXTITE AB830 (Fast Cure), NEXTITE AB832 (Medium Cure), NEXTITE AB835 (Long Cure). NEXTITE AB200 Series - NEXTITE AB200 (Fast Cure), NEXTITE AB210 (Medium Cure) are also great options for bonding aluminium to itself and other dissimilar materials.

Instant Adhesives (Cyanoacrylates)

Strengths	Extremely fast fixture, high shear strength, no mixing (single part), great for high-speed production lines various grades available for different adhesive needs.
Limitations	Limited gap filling capability without activators, lower impact and peel strength compared to other structural adhesives, surface preparation is necessary.
Most Suitable	We recommend using one of our premium surface insensitive grades or rubber toughened grades for best results when bonding aluminium, although all grades of NEXTITE Instant Adhesives will bond Aluminium if prepared correctly. For General Purpose: NEXTITE 501 (Medium Viscosity) For Impact Resistance: NEXTITE 535 (Medium Viscosity, Clear, Toughened), NEXTITE 580 (Medium Viscosity, Black, Toughened)

Epoxy Adhesives

Strengths	Epoxies both one part and two part are an excellent choice for bonding aluminium. They offer the highest shear strength when bonding aluminium to itself, when bonding to dissimilar materials consider a toughened epoxy. Great chemical resistance, suitable for applications that require high temperature resistance.
Limitations	Generally epoxies are fairly rigid and have low fatigue and impact resistance (excluding toughened grades), long time to fixture or a baking process required, surface preparation is required
Most Suitable	NEXTITE EA1100 is a good choice when bonding aluminium to itself.

Structural Polyurethanes (2 Component)

Strengths	Structural adhesive, good flexibility, high peel strength, good impact strength, dissimilar material bonding, gap-filling
Limitations	Long fixture time at room temperature, strong odour, not as high strength as MMAs or Epoxies
Most Suitable	NEXTITE SP300 is suitable for bonding Aluminium to itself and dissimilar materials.

UV Adhesives

Strengths	Extremely high clarity joints that are bubble and blush free, easy to do extremely high-quality joinery, high joint strength, set the adhesive whenever you are ready.
Limitations	Limited outdoor environmental exposure, higher set up cost, material MUST be UV transmissive to cure UV adhesive. Aluminium blocks UV light, if curing through a clear substrate onto Aluminium, UV can be a suitable option.
Most Suitable	NEXTITE UV419 is a thick viscosity slightly flexible, suitable for bonding metal to a transparent material. NEXTITE UV1700 is a gel UV adhesives suitable for bonding metal to a transparent material.

MS Polymers

Strengths	Excellent flexibility, toughness and impact resistance, good weather resistance, vibration resistant, easy application (single part)
Limitations	Lower structural strength, slower curing (especially thick bondlines), moisture dependent curing, temperature limitations.
Most Suitable	NEXTITE MS300 is suitable for bonding Aluminium to itself and other materials where a flexible bond or seal is required.

Construction Adhesives: Silicones, Polyurethanes (single part) and Acrylic (single part)

Strengths	Budget option, fairly versatile, generally fairly flexible, weather resistant, gap filling, easy to apply (single part), sealing properties
Limitations	Low strength, slower curing (especially thick bondlines), temperature limitations, substrate limitations, UV and Water resistance varies product to product.

 

What industries is Aluminium used in?

Aluminium is one of the most widely used metals due to its unique properties. It is used across a wide range of industries including:

• Aerospace and aviation
• Automotive and transport
• Building and construction
• Electronics and appliances
• Marine
• Manufacturing and industrial equipment
• Signage and display

Any challenges with bonding Aluminium?

As mentioned above aluminium has an invisible oxide layer on its surface that forms quickly as soon as it's exposed to air. 

Adhesive chosen must be suitable for the application, especially when aluminium is being bonded to dissimilar materials to allow for thermal expansion.

Galvanic corrosion can occur when aluminium comes into contact with a dissimilar material in the presence of moisture. Using an adhesive to join your aluminium to other metals instead of using fasteners will reduce this from happening. Another option is powder coating or anodizing. 

Summary

Choosing the best industrial adhesive to bond Aluminium comes down to understanding the application requirements and performance required from the joint.

If you would like to speak to our expert team about your next project, please contact us for tailored advice and product recommendations to suit your application.