Bonding Aluminum with Epoxy

What are people's experience bonding aluminum to other materials with epoxy resin, in general or in boatbuilding applications in particular?

The Gougeon book on West System boatbuilding give sthe drill on wet sanding the aluminum surface in mixed resin immediately prior to bonding to minimize the affects of immediate oxide formation on the aluminum surface if exposed to air.

Andy Marshall, in his handbook Composite Basics (geared to homebuilt aircraft) says if the aluminum in't prepped with a certain mil-spec process developed by Boeing ANY bonding of aluminum with epoxy resin WILL fail. The question isn't "if", but "when", and "when" isn't predictable.

 

Again I can only speak to aircraft, but epoxy is rarely used in bonding metal parts to any surface on large aircraft. In some areas small skin repairs are done, the bonding area is chemically etched and primed with alumiprep and alodine or similar as found here.
http://www.wicksaircraft.com/gotopage.php?page=50 A film epoxy is used with vacuum bagging and heat.
Most aluminum fittings are bonded with a polysulfide and mechanically fastened. Even with the fasteners removed it can be a very difficult job to replace a damaged fitting installed this way.

Gary

 

I believe that there is a toughened epoxy adhesive that can be used for this purpose. The epoxy is toughened with very small rubber balls that help to prevent crack migration. I am told that you should apply it with a large radii on the edges of joins and that it has been used to join fittings to carbon masts.

Any body have any more comments of this method? Personal experience perhaps?
Brett

 

Chris Krumm ---

I think Andy Marshall is correct. Due to the aluminum oxidizing the bond strength drops to 0 over time.

I have heard that there is an alodine process that works. I have been unable to find the cleaner (perhaps due to lnot looking hard enough).

I am testing 3m 5200.

 

Aluminium like all metals will only oxidise if at has access to oxygen, and a good glue joint should prevent this.

Plenty of alumninium cars are glued together and the additional rivets are there only to hold th joints in place while the glue cures, after that there is little to be gained from removing them so they are just left in place.

Araldite 2015 has German type approval for bonding Aluminium in the construction of Marine craft.

If you need more info you could contact araldite directly as they are generally very helpful.

I have used this on my prototypes with no sign of any faliures yet.

All the best

Gareth Roberts
www.fourhulls.com

 

AN OPTION

We have used Lord adhesives for aluminum sign fabrication for years. I like the low prep requirements and fast working times.
I allways maroon scotchbrite and wipe down with a degreaser like PPG has I think it is called DX685, anyway acetone works fine too.
Its a 2 part epoxy with a 4 to 1 ratio that requires a special dispensing gun and static mixing tips.
Gun $70.00
cartrige $30.00 (13.66 oz or 405ml)
mixing tips $1.45 ea
Thats what we sell it for! This is not a plug but I have a hard time getting my guy's to buy a 70 dollar caulking gun on the other hand i've never had one come back either. Check with your local sign supply house or some of the larger automotive paint stores.
they should be able to get you set up. I think Hilti makes a simular system too.

403/19 work time 2-4 min-full cure 1 hour
406/19 work time 6-10 min-full cure 4 hours
http://www.lordadhesives.com/sign-n-display/substrates.asp
hope this helps
8Knots

 

bonding alluminum

See 3M website you will find information on scoth weld 2 part epoxy glue for metal. I used this product several time with success. We used this product on Aircraft Engine (Turbo fan case ) with great success.
I used this product instead of rivets on a free standing mast to joint the sleeve in the midle of the mast and no regreat.

 

aluminium epoxy bonding

Does anyone on the forum has more information on this subject?

The last comment by Bob Stuart made me skip any previous thoughts about bonding aluminum with epoxy in a marine environment.

From http://www.ihpva.org/pipermail/hpv-boats/2005q1/005404.html

 

Although I posted "I have used this on my prototypes with no sign of any faliures yet." regarding Araldite 2015, since that post over three years have past and I regret to report that I did get some failures.

Some of the failures were at pretty low loads, some of the joints are still strong despite being tested to very high loads, it is this lack of consistency that led me to abandon this method.

It could be the surface preparation, anodise, abrade, acetone. But I felt that some of alternative treatments advised in the Araldite literature were just far to hazardous to contemplate.

I would love to get this method to work consistently so if anyone has better practical experience I would be keen to hear from them.

Gareth

 

Corrosion and seam width

Great to hear about your experiences Grob.

Key to a good and lasting bond seems keeping the aluminum out of contact with water and air. As mentioned by Bob even epoxy lets pass water vapour.

It seems to me that glue seam width (the thickness of the glue between the bonded aluminum, there must be a better word) plays a role here. The adhesives used in the airplane industry require a seam as thin as possible. A thin film of adhesive will let the vapour pass at a slower rate than thick one. The tolerances used in the airplane industry are impractical (expensive) for boatbuilding.

Even the best surface preparation does not prevent corrosion.

I a afraid my dreams of ply/epoxy/aluminum building are down the drain.

 

West systems reply

Just found this in my inbox, a reply from west systems:

 

From the west systems technical manual

http://www.wessex-resins.com/West_System/using_west_system_technical_manual.htm

Will make the request

 

Part of the request

request

 

marine grade aluminium oxide properties

Seawater resistant aluminum still relies on an oxide layer to prevent further corrosion. Can it be this oxide has better mechanical/bonding properties than other aluminum alloy oxides?

Corrosion at the bond surface will still destroy the original bond between the bare aluminum and epoxy. Puzzled.

 

The reply:

Unfortunately the Lloyds certification does not contain any details.
The "quite an extended period of time" does not take away my worries.