aluminum bonding to carbon fiber 1

[keebs]

I am having issues bonding an aluminum plate to a carbon fiber structure. It is a 2"x3" aluminum plate bonded inside a carbon fiber square. The aluminum plate sees a fair amount of shock due to the application. The seperation occurs between both the aluminum plate and the adhesive, and the adhesive and carbon fiber.

 

[JimMetalsCeramics]

You could solder it.

Is the carbon fiber structure pure carbon or carbon in a polymer?

 

[keebs]

This is a carbon fiber laminate. Pure strands of carbon fiber held together with an adhesive. Will the solder attach to a laminate?

 

[TVP]

What type of adhesive are you using? What manufacturer? The latest generation aluminum-filled toughened epoxies from 3M (Scoth-Weld 2214) have the best bonding to aluminum. Loctite Aerospace (formerly Dexter) and Hexcel also make suitable adhesives.

 

[keebs]

Thanks TVP on the update to the 3M products. Currently we are using a PRO-SET adhesive, is great for laminates. The lap shear is 2864 psi and the tensile adhesion is 3415 psi on aluminum. I am not sure how this compares to the 3M products.

 

[JimMetalsCeramics]

Since its adhesive-based, it's difficult. But you could solder after thin film metallization. For now, you should stay with trying other adhesives and surface preparation methods (e. g., silane).

 

[TVP]

2214 has maximum overlap shear strength of 4500 psi on aluminum. The strength decreases if greater toughness is needed, or if high temperature performance is required. See the following data sheet:

http://www.3m.com/us/mfg_industrial/adhesives/pdf/2214dp.pdf

 

[keebs]

I am going to continue using the adhesive and roughen the aluminum surface with a steel shot. I found several companies that will media blast with different materials.
This should give a better surface for the adhesive to bond too.

 

[keebs]

Thanks TVP for the link.

 

[JimMetalsCeramics]

It sound like you need an adhesive promoter. Speak to the adhesive companies. One option might be silane.

 

[bisonlee]

you should also be careful of the corrosion problem you may have long term due to the effects of galvanic corrosion. if you look at a galvanic table you will see that carbon and aluminium are at almost opposite ends.

 

[MintJulep]

Surface preparation is always an important (and often overlooked) factor with adhesives.

How much is "a fare amount of shock"? It could be that the loads involved are higher than you believe?

Work with an adhesive supplier. I would suggest the same manufacturer that makes the adhesive used in your carbon-fiber laminate, as they should have an advantage in knowing what will stick best to that.

Could the plate be molded in when the laminate is produced rather than applied as a secondary operation?

 

[rerig]

Due to the galvanic action between Graphite and Aluminum, most composite layups will use a thin (type 120)Fiberglass ply between the Graphite and the Aluminum. This is the barrier to the galvanic action. The Fiberglass is not normally accounted for in the strength calculation. The resin matrix requires a compatable film adhesive if co-cured onto the plate. Use an film or paste adhesive if bonding a pre-cured laminate to the Aluminum Plate.

On aircraft, we bond thin (0.012 - 0.020) aluminum sheet to graphite parts with the FG Barrier ply and an adhesive or a thin coat of sealant. This is for lightning protection. It's done on most Flight Controls all the time.

 

[Kiwikid]

It looks like your problem is primarily the adhesive if you are loosing adhesion to both the carbon fibre and the alloy plate.

If finding a suitable adhesive that bonds well to both materials is a problem then a sandwich solution may be your answer eg; adhesive 1 between the plate and another material and adhesive 2 between the material and the carbon fibre.

Are mechanical fasteners an option?

If you can solve the adhesive problem then perhaps increasing the surface area on both the carbon fibre and plate bonded surfaces could improve strength. East - west and north - south channel groves would achieve this.