Secondary bonding and design?

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#21

Okay, that is a little bizarre as it should bond reasonably well with very little prep.

I guess you need to check the alloy prep, the solvent & wipes you may be using, and what method are you using to compress the alloy to the surface, if you have air entrapment, the humidity and temperature plays a part… It could well be a number of things, combined!

If you use certain adhesives and over compress - then the bond strength is drastically reduced. 0.2-0.5mm is ideal for a “standard” structural adhesive.

The adhesives I have recommended work in a wide range of bond lines - Araldite’s optimum bond line is 0.05mm to 0.1mm
It will work with larger gaps as well, so do not be put off.

#22

I bond ali to carbon all the time for high stress motorsport applications. Peel strength has never ever been an issue, no matter the geometry.

#23

Hanaldo, I think what you said about the resin thickness was right in terms of what is causing my specific issue. I guess the laminating resins I use are just not suitable for adhesion to aluminum.

Based on your advise I have been experimenting with some of my thicker resins (the ones that stay put when you apply them) and they produce a better bond. I can still peel it off with a chisel but it’s a big improvement. When combined with a proper surface treatment I could see it working fairly well.

I haven’t tried using a thicker resin to stick cf to the aluminum yet. I am waiting for delivery of a rubber roller to ally it smooth and evenly as this is a problem for me with thicker resins. Any lumps show through with cf on flat surfaces.

Out of interest, with cf / aluminum bonds for car parts, are they affected by changes in temp and the metal expanding? I imagine heat is a consideration for anything near the engine.

#24

Yeh definitely. For most motorsport applications I use Araldite 2015 as it remains slightly flexible, which helps it resist problems from expansion and vibration.

I also use 2014 quite a lot due to its higher temperature and chemical resistance, as well as Plexus methyl methacrylate. But those two I generally use for composite to composite joins, I tend to only use 2015 for ali to composite.