Bonding Aluminum with Epoxy

[Dresca]

Mechanical & chemical

It seems to me from scanning this thread that most people when traditional mould building rely on a mix of Mechanical and Chemical bonding. I did read somewhere that even in ancient Polyester laminates some 10% of the laminate still remains active, is this correct?

I have bonded onto 12 month old laminates with pure polyester orthos, its not a strong joint, but with some aggressive sanding it seems to hold. Surely when mould making (the traditional way), having laid up a skin coat, then every week or or so adding a few more layers & sanding this equates to a mix of mechanical & chemical. Personally I don't have time for this way of mould making I use the heavy filled BP catalyst cured tooling resins, but as far as I understood it I thought thats the way many folk made forms?

I'm about to use a Urethane modified resin thats supposed to help bonding onto cured polyester laminates with a 10-20% addition to normal laminating polyester resins. I'd be really interested to hear is anyone has ever tried using this kind of material?

 

[SeaweedSam]

Hope readers of this thread get this far.. I bonded an aluminum plate 1/4" x 12" x 12" to the fiberglass hull of my boat to create an area for outboard motor mount. Since I thru-bolted it anyway and I was mainly concerned with a strong watertight seal I used a tube of 5200 I had laying around . There was minimal sanding on the glass and a quick hand cleaning with acetone and no prep at all on the aluminum plate. I do not know if it was coated or not but it did not appear so , although it looked new and shiny and I could not say what type of plate it was as it had been given to me for this purpose several months before. It been there nearly 5 years on a boat floating all day every day in salt water . Last year I attempted to dismount it to relocate it .. MEBS! I pried, pushed, drilled a "grab hole" for a large bolt, hammered it a bit ...no good!! I dont have any way to measure "shear", "peel" or any other fancy term for failure but I can say that suckers on there short of cutting the entire section out and doing a repair. BTW I hung a 90lb 2stroke Johnson on it so it definitely got some vibration and flex. Goodluck to all SAM

 

[mydauphin]

5200 will hold aluminum fairly well, but surface area must be large, and best to have freshly cleaned aluminum. Same for epoxy, it take corrosion a long time to get to center and cause release.

 

[SeaweedSam]

Thanks for the reply .. You're right about the 5200 . Ive never attached anything using 5200 that did not require considerable effort to remove. Old , sunbeat 5200 can be a real bear . BTW I'm considering hull(s) of aluminum sheet bonded to a standard laminated ply epoxy bulkheads with minimal stringers. I would "form" one long sheet over the framework and attach fore and aft "dory style" since that configuration gives proven stiffness and form ala Wharram. All plumbing and electric would be inboard run through the wooden bulkheads via PVC tube or equal. standing rigging to be Dyneema or like run through blocks to be fabricated with wood carbon fiber laminates. The goal is to have as few dissimilar metals on the boat as possible and nothing but the hull, drive and rudder touching the water. Thanks again Sam

 

[dinoa]

I am surprised that methacrylate glues are not mentioned more. (Peter did...)

Many aluminium parts are succesfully bonded with methacrylates in marine, airospace and automotive environment.

I am familiar with the ITW Plexus range. They carry a primer (PC-120) which etches the oxide layer. Then a durable glue bond can be made using MA-300, MA310 or MA420.
However, methacrylates demand more accuracy then epoxy glues. Temperature is a factor, mixing is more critical, and bondline thickness needs to be observed as well (1mm for Plexus). Most manufacturers have all the procedures in the specsheets.

I have had some aluminium bonded parts in my osmosis tester (submerged, 60 degrees C) which never came apart. The must have been there at least for 6 months.

When using epoxy to glue aluminium, keep track of the elongation at break. This should indeed be high (thank you Peter). Normal epoxies do not have an elongation which is that high, so use a "rubber toughened" epoxy, and even then check the spec sheets.

From my experience Plexus is the best way to go. Applying the PC-120 primer is easier to accomplish than phosphoric acid etch that should be done with epoxy. http://www.itwplexus.com/

Dino