On the G-flex, I have some, know it well. In your original para, you say:

"'ve come up with a tentative idea for the metal bonding. i expect that if i coat my metal parts with a smooth coat of g-flex and let it kick, i'll be able to simply start gluing my project to the tube with much less worry. i've heard of people using etching primer or something of the sort, but g-flex is relatively new and i've heard great stuff about it. dad says they use it a ton at the boat yard."

I didn't get from that why you are using it other than you think it might be good. I figured you were either concerned about enhancing adhesion or the possibility that the different expansion rate of materials might fail the bond, and G-flex being flexible would deal with that. In your most recent post it sounds like you are worried about galvanic? It would help if I knew what is the issue. My assumptions are:

- That a flexible layer is not essential, there are many products where carbon is bonded right over aluminum from mountaineering ice axe shafts to Olympic archery arrows and while the materials are dissimilar there does not appear to be an issue of some kind of shear induced separation as a result of dissimilar materials.

- My assumption is that G-flex does not improve the performance of carbon when used as a boundary layer for adhesion, and this is sorta anti WEST with all their performance emphasis on the need to have hard epoxies. But that is just my guess, and it could be a good question for their techs. In part I am just relying on the idea above that there are lots of product that work well pre-G-flex. Should be easy to source g-flex stats on bond strength.

- On the corrosion issue I rely again on the idea that it doesn't seem to be a problem, particularly on dry land, but then suggesting that you prep the surface with epoxy can't really hurt anything. But if it were me I would be prepping with 105/205. Again, the kind of question you could ask their techs.

WEST, got off to a good start with the wood epoxy thing, and promoting epoxies that could not be formulated (like g-flex) as 1-1 mixes. They emphasized hardness and creep resistance. While I believe they were right in that, they left themselves open to competitors who have hammered them on the "fact" that their epoxies are too hard, and crack etc... Nonsense, but it has gained currency. However, there are applications where the durometer of their epoxies is too hard. If you look at this aluminum bonding video, you can see that they are selling G-flex as an improvement over silicone caulking. Obviously it is much tougher than silicone, but something like oil canning in a boat plate could break out a hard epoxy, while silicone would not have the adhesion or penetration or durability of epoxy.

http://www.westsystem.com/ss/g-flex-demo/

Another example from their info is a guy who used g-flex alone to bond guides to a fishing rods, without using thread whippings. This is an interesting case, because the carbon fiber rod blank would be a very poor candidate for g-flex lamination but the extreme deformation it is capable of creates a micro environment where just gluing guides onto the blank with hard epoxy might not be successful.

I don't think you will run into trouble with what you are suggesting because there are many square inches of bonding surface on either of the tubes one needs to bond. I have bonded many golf club heads to shafts with specialized golf epoxies that are 1-1 mixes. Some of these have proved brutal to dismount, in one case requiring so much heat the thing went off like a Roman candle. In these structures (tube inside of tube), the bonds tend to be very reliable.