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Epoxy isnt bonding to aluminum

RVFan671

Well Known Member
I am working on emp fairings for my rv10. I decided I wanted more grip for the blind rivets so put .025 strip of aluminum about .5" tall along the fairings. I used west 406 with the west 105 and 206 hardener. When I was final drilling the holes on the emp (originally just drilled to 3/32 then final to #30) the strip of aluminum just came right off.

I scuffed the strips with 120 grit sandpaper along with the fiberglass and cleaned both with acetone before using my mayonaise consistancy mixture of epoxy and 406. The epoxy didn't bond all to the aluminum. Any suggestions what went wrong?
 
Sand the aluminum with 60-80 grit and fiberglass with 80. Clean with mineral spirits until all black stops coming off aluminum. Clean clean clean. Cleaning FG with acetone can reduce the sanding marks to less bite.
 
40 grit

As mentioned. The aluminum needs some tooth. I even go 40 grit. Clean thoroughly.
I prefer a more agressive epoxy. West G-flex. I spread a thin layer neat then mix in flox and cabosil to the thickness you described. Apply and cleko. I wipe clekos with wax so they dont stick.
Not sure but 405 is a fillet blend. Doesn't sound structural. I would use flox.
 
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Etch

You have to etch the alu after the sanding, just as if you were painting. Use a two part system with a cleaner and etch. If it is not etched it will never hold. Another trick is to drill very small holes through the alu to let some of the epoxy flow through to the other side. this forms a sandwich of the alu in the epoxy which enhances the bond.
 
The epoxy didn't bond all to the aluminum. Any suggestions what went wrong?

You might want to try Hysol. My Tech Counselor recommended this for the windscreen fairing and I have to say it’s bulletproof. Made several test samples of aluminum to plexy and aluminum to fiberglass, and you literally had to destroy the sample before they came apart. West system epoxy is a great product but Hysol seems to be indestructible for bonding dissimilar materials. Either way, as mentioned, prepping the underlying material is key.
 
Etch

I think it recommends an acid etch in the plans for the -10, around the windscreen, where the epoxy bonds to the aluminum.

Page 45-18 step 9 calls for a phosphoric acid etch after sanding the aluminum.

It would appear, as previously posted, sand, etch, and clean, clean, clean!
 
Thanks all! I will pick up some 80 grit and give it the etch bath. Luckily I was careful and the strips arent fully delaminated so I'll get my rivets in once I finish up.
 
It is a long while since I tried to bond fibreglass and aluminium. The problem is that aluminium produces an oxidised layer practically instantaneously, so that the longer between roughing up the surface and applying resin, the greater chance of failure.
I have succesfully bonded them by using a small quantity of resin as a lubricant for the final roughing up of the surface. The theory being that the surface is abraded and instantly encased in air excluding resin.
It worked for me.
 
I am working on emp fairings for my rv10. I decided I wanted more grip for the blind rivets so put .025 strip of aluminum about .5" tall along the fairings. I used west 406 with the west 105 and 206 hardener. When I was final drilling the holes on the emp (originally just drilled to 3/32 then final to #30) the strip of aluminum just came right off.

I scuffed the strips with 120 grit sandpaper along with the fiberglass and cleaned both with acetone before using my mayonaise consistancy mixture of epoxy and 406. The epoxy didn't bond all to the aluminum. Any suggestions what went wrong?

I scuff my aluminum with scrotbrite pad, etch and alodine the surface. I found out with this treatment I can bond any type of epoxy to the surface, from 5-min type to the West System laminating epoxy. One extra step I do is to also clean the surface to be epoxy bonded with alcohol just before the application of the resin. I stay away from all types of solvents because depending on the supplier, some solvents can leave behind residue that inhibit the good bonding between the aluminum and epoxy resin.
 
I am working on emp fairings for my rv10. I decided I wanted more grip for the blind rivets so put .025 strip of aluminum about .5" tall along the fairings. I used west 406 with the west 105 and 206 hardener. When I was final drilling the holes on the emp (originally just drilled to 3/32 then final to #30) the strip of aluminum just came right off.

I scuffed the strips with 120 grit sandpaper along with the fiberglass and cleaned both with acetone before using my mayonaise consistancy mixture of epoxy and 406. The epoxy didn't bond all to the aluminum. Any suggestions what went wrong?

Be realistic about what you can expect from that bond:
https://www.epoxyworks.com/index.php/aluminum-adhesion/

West System can produce 7-8 ksi polymer, but the bond to well prepared aluminum without any oxide (tricky) will end up in the vicinity of 2 ksi. Your drill, on the other hand, has to exceed ~70 ksi locally. Once started, delamination propagates very quickly, as you found out the hard way. Lots of stress on that surface--epoxy shrinks as it cures. It's like trying to drill tempered glass.

Chromate conversion (alodine) can increase the bond strength by a few to ~10% (e.g. see here). More importantly, if converted immediately after etch it keeps the oxide away and gives you time to dry everything and work slowly. Use gloves and don't apply any solvents after alodine. Drill the holes in aluminum prior to bonding, then back-drill through the glass after cure with a diamond burr.

Or, you could just Stick To The Plans (TM) and pull the correct rivets into fiberglass like everyone else. :D
 
We did A LOT of aluminum bonding when building the Cozy MKIV. I remember specifically written in the Rutan plans when instructed to prep the aluminum for bonding to use nothing coarser than 220 grit when sanding the aluminum. I only use 40 grit Zircon to prep sand the cured fiberglass in preparation for bonding or additional fiberglass lay-ups. Acetone is an excellent choice for wiping down the aluminum. Use nothing but air to clean off the sanding dust from fiberglass parts. If you still see shiny areas in the fiberglass after sanding,,,sand some more until you don't. I ONLY use West System epoxy for fill. For structural and bonding purposes, MGS epoxy system is a much better choice IMHO. I always have both on hand.
 
In the RV fiberglass class one suggestion was to use a high peel strength epoxy for aluminum to fiberglass. We even did some testing in class and the stuff bonds to the aluminum. Aluminum breaks before the structural adhesive. Plan on using it for when the windshield goes on.

Aeropoxy ES6247 HIGH PEEL STRENGTH EPOXY ADHESIVE

May be overkill for the emp fairings but another solution to keep in mind. (Will absolutely agree with he sanding and cleaning suggestions offered earlier.).
 
... use a high peel strength epoxy for aluminum to fiberglass.
You done broke the code. I built a fiberglass aircraft with a number of aluminum inserts and never had any luck bonding epoxy to aluminum - even after sanding, etching, and alodyning. I tried it all and the ONLY thing that worked was structural adhesive like Hysol.
 
I would recommend the West Systems G-Flex epoxy for this. I just fixed a gear leg fairing where the hinge that was riveted in tore out. A little G-Flex under the hinge after filling in the old holes, then riveted while wet. It isn't coming loose again! That stuff is amazing and it won't pop off, since it remains flexible after curing.
 
Ditto for G/flex and also, 3M's 2216 B/A. These are effective with aluminum. I have seen test results of my samples using G/flex and while all I have are strength tests, not fatigue or post-environmental exposure tests, they do indicate a good solid bond.

This is the version I've been using.

Dave
 
It is a long while since I tried to bond fibreglass and aluminium. The problem is that aluminium produces an oxidised layer practically instantaneously, so that the longer between roughing up the surface and applying resin, the greater chance of failure.
I have succesfully bonded them by using a small quantity of resin as a lubricant for the final roughing up of the surface. The theory being that the surface is abraded and instantly encased in air excluding resin.
It worked for me.

+1. I did a lot of sample testing on bonding aluminium to fibreglass using epoxy resin. I tried virtually everything that has been recommended in this thread and the only technique I found that produced a really positive bond was the one suggested above. If you clean the aluminium surface and then brush on some pure epoxy and then sand the aluminium through the wet epoxy with a high grade 80 grit the aluminium cannot oxidise. Bare aluminium oxidises virtually immediately and the epoxy will not bond properly to aluminium oxide. When you sand through the newly applied liquid epoxy you create fresh mechanical abrasions that cannot oxidise. If applicable, drilling some holes in the aluminium to let the epoxy flow through also increases the mechanical bond strength.
 
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