Bonding Aluminum with Epoxy

[Chris Krumm]

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.

[duluthboats]

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

[BrettM]

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.

[grob]

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

[8knots]

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-...substrates.asp
hope this helps
8Knots

[Tangara]

Originally Posted by Chris Krumm

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.

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.

[SeaSpark]

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-b...q1/005404.html

> I last posted a question regarding epoxy and aluminum. Would this
> product be better than epoxy with aluminum that has not been
> etched/prep'd? Has anyone tried this product?
>
> "Devcon's Metal Welder adhesive has been reformulated to provide a
> longer working time (5-6 minutes at 72° F), according to a company
> spokesperson. The new formulation is a non-sagging 10:1 methacrylate
> with a mixed viscosity of 55,000 cps. Glass beads throughout the
> activator optimize adhesion by ensuring a consistent gap of 20 mils
> between bonded surfaces, the spokesperson stated. Designed to bond bare,
> painted, plated, or galvanized metals to each other or to thermoplastic
> or composite assemblies, Metal Welder requires no primers and minimal
> surface preparation."

Devcon claims are usually reliable, but if the problem is bonding to surface
oxidation, I don't see how it would help. For reliability, the aircraft
industry is the place to check for certification, and they use the 2-part
kit with epoxy.

You can get an excellent temporary bond just by sanding, and then finishing
the sanding with the surface wet with epoxy. It is messy, but it worked for
White Lightning, the 1st HPV over 55 MPH. Unfortunately, even epoxy, the
most impervious of the options, still passes minute amounts of water vapour.
When this arrives at the aluminum, the hydrogen gets jilted and you wind up
with an oxidized surface (failing bond) in about two years.

Cheers,
Bob Stuart

[grob]

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

[SeaSpark]

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.

[SeaSpark]

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

We however can advise that epoxy is absolutely ideal for bonding of wood to aluminium, providing that good surface preparation is carried out as per the free WEST SYSTEM "User Manual and Product Catalogue", (Clean - free of any oil, grease or other contamination, dry - low moisture content, and abraded - if hand sanding use 80 grit paper or coarser, if power sanding then use 40 grit paper or coarser). Specialist preparation for a variety of different substrates can be found in our WEST SYSTEM "User Manual and Product Catalogue".
Aluminium - Non-anodised material must be degreased and either thoroughly abraded or chemically etched, (sulphuric acid/sodium dichromate solution or branded aluminium etch compound).
Anodised aluminium and anodised aluminium alloys - must be bonded as quickly as possible after degreasing and abrading and certainly within 30 minutes.
Hard anodised aluminium alloy - must be stripped by abrasive blasting or by etching in sulphuric acid/sodium dichromate solution or branded aluminium etch compound. Unstripped metal is not suitable for bonding.

Epoxy is a very strong & durable material and has several uses. Epoxy is ideal for use in a bonding application of timber to aluminium and is far stronger than timber itself and therefore if failure is to occur it would be within the timber.

[SeaSpark]

http://www.wessex-resins.com/West_Sy...cal_manual.htm

The WEST SYSTEM epoxies have been approved by the Lloyds Register of Shipping following an extensive test programme which involved bonding wood, glass reinforced plastic (GRP), mild steel, aluminium and combinations thereof. Specific details of this accreditation are available on request.

Will make the request

[SeaSpark]

request

I am worried about the aluminum corroding at the bonding surface after
making the bond, even epoxy allows minute amounts of water vapour pass
coursing corrosion at the aluminum surface. At the edge of the bond
the aluminum will always we able to corrode coursing a small crack in
witch water can collect.

I am very curious about the details of the accreditation.

[SeaSpark]

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.

[SeaSpark]

Please find enclosed a copy of our Lloyds certification.

Unfortunately no material is completely impervious to moisture and over time moisture will eventually reach the aluminium surface. WEST SYSTEM epoxy will provide superb protection against moisture and protect the aluminium surface for quite an extended period of time, providing the relevant preparation is carried out. Unfortunately we do not have any further test data to support how long we expect a coating to keep moisture away from any particular surface.

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