Discover in this article the best adhesives for bonding metal
Which is the strongest adhesive?
In terms of tensile strength, the strongest adhesives are epoxy adhesives, specifically heat-cured one-component epoxy adhesives. They have a tensile strength of 35-41 N/mm² (5100-6000 psi).
What are the best adhesives for metal bonding?
The tensile strength of an adhesive simply indicates how strong the adhesive is once cured. It doesn’t tell us how well it bonds to different substrates. In terms of tensile strength, the highest values are found in metal-to-metal bonding cases. The adhesives that perform best are:
One-component epoxy
One-component epoxies adhere well to metals and offer a great alternative to welding, providing high shear, impact, and peel strength. They exhibit excellent resistance to chemicals and extreme temperatures. The shear strength on steel can reach up to 41 N/mm² (6000 psi). Please note that the surface treatment of steel and the bond gap can affect the maximum strength.
There are also low-temperature curing products for heat-sensitive parts, but they do not provide the best adhesion to plastics and other materials.
Due to the bonding properties of one-component epoxies, if you want to undo the bond, you will need to heat it to over 250°C to separate the parts.
Acrylic structural adhesives
Methyl methacrylate and acrylic structural adhesives also have very high tensile strength and bond well to metals and plastics, even some low-surface-energy plastics that are challenging to bond. They are also highly resistant to chemicals and temperature. To remove the cured adhesive, it must be heated to over 200°C to soften it and separate the parts with hot adhesive. Tensile strength varies depending on the type and range but often exceeds 28 N/mm² (4000 psi).
Two-component epoxy adhesives
Two-component epoxy adhesives have roughly the same tensile strength as many structural acrylic adhesives. The added advantage of two-component epoxies is that they bond well to a broader range of substrates and cure at room temperature. They adhere to many plastics, especially composites. To break the bond, two-component epoxies must be heated to over 120°C to soften them, and the parts should be separated while the adhesive is still hot. Tensile strength is approximately 20-30 N/mm² (2900-4400 psi).
Cyanoacrylate adhesives
Cyanoacrylate adhesives, especially pure methyl cyanoacrylates like Permabond 910 and impact-modified ones like Permabond 731, have exceptional strength on steel at 30 N/mm² (4400 psi). They do not have the same chemical and thermal resistance. Epoxy and acrylic adhesives provide better impact resistance than cyanoacrylates. The advantage is that cyanoacrylate can be easier to remove. Warm water and soap are sufficient to separate surfaces. In some cases, temperature (100-120°C) can also be used with materials that can withstand it.
Anaerobic adhesives and sealants are also ideal for metal (they are designed for metal only). Some may wonder why we haven’t mentioned them earlier. They are strong and suitable for metal, so theoretically, they could rank higher, but in this article, we focus on bonding. Although anaerobic adhesives bond, they are generally used as thread lockers, retaining compounds, thread sealers, and gasket makers.
This is a brief overview of possible solutions for metal bonding. Contact Mercouris for information on the best product for your specific application.